1. William Blair 25 th Annual Growth Stock Conference June 16, 2005

2. 2 Statements included in this presentation or in the oral comments made as part of this presentation may contain forward-looking statements, including but not limited to statements of the Company’s plans, objectives, expectations or intentions, that involve risk and uncertainties. The Company’s actual results may differ significantly from those projected or suggested in any forward-looking statement due to a variety of factors, which are discussed in detail in the Company’s filings with the Securities and Exchange Commission. Forward-Looking Statements

3. 3 Our Interests are Aligned with Clients and Patients: To make the use of prescription drugs safer and more affordable

4. 4 More Number of Drugs Fewer Alignment –Formulary Management Therapy Class We Provide Flexible Management of the Supply Chain 1. Select number of drugs in therapy class # of drugs # of drugs # of drugs # of drugs

5. 5 More Number of Drugs Fewer Alignment –Formulary Management Therapy Class We Provide Flexible Management of the Supply Chain 1. Select number of drugs in therapy class 2. Determine formulary control Benefit Options # of drugs # of drugs # of drugs # of drugs Open Differential Co-pay Closed

6. 6 More Number of Drugs Fewer Benefit Options Impact on ClientImpact on PatientImpact on ESI Lower drug cost More choice Lower co payment More choice Higher Profit/Rx More Flexibility Alignment –Formulary Management Therapy Class We Provide Flexible Management of the Supply Chain 1. Select number of drugs in therapy class 2. Determine formulary control 3. Drive towards lowest overall cost # of drugs # of drugs # of drugs # of drugs Open Differential Co-pay Closed Lowest Overall Cost

7. 7 Alignment - Retail Network Management States Available Pharmacies Most Inclusive Network Most Restrictive Network TRICARE Access Minimum CA 5,6445,0713,881283 NY 4,4444,2241,829300 TX 4,2363,8211,827579 FL 4,0203,6701,966469 PA 2,9702,8251,687432 Greater Management Higher Profit/Rx More Flexibility Lower co payment More choice Lower drug cost More choice Impact on ESIImpact on PatientImpact on Client Higher Profit/RxLower co paymentLower drug cost Impact on ESIImpact on PatientImpact on Client

8. 8 Impact on PatientImpact on ESI Lower drug costLower co paymentHigher Profit/Rx Alignment – Clinical Programs Clients using step therapy realize on average a 2 percentage point increase in generic utilization Plan Designs Encourage Greater Use of Generics and Preferred Low-cost Brands

9. 9 Alignment – Home Delivery Impact on ClientImpact on PatientImpact on ESI Lower drug cost Choice Lower co payment Choice Higher profit/Rx We Offer Highly Efficient, Cost-effective Home Delivery

10. 10 * Represents network claims plus 3 times home delivery claims –home delivery claims are 90 days vs. 30 days in the network. Excludes UHC claims Increased home delivery penetration Home Delivery Helps Manage the Cost of Maintenance Drugs Alignment – Growing Demand for Mail

11. 11 Alignment – Generic Utilization Impact on ClientImpact on PatientImpact on ESI Lowest drug costLowest co paymentHighest profit/Rx Source: From public filings Express Scripts Leads in Generic Utilization

12. 12 ESI Analysis Represents over 20% of 2004 branded drug sales Our Clients and Members Will Benefit From a Growing Generic Opportunity Alignment – Growing Generic Opportunity

13. 13 100%$35 Total 19%3.5Other 1%0.5Growth Hormone 1%0.5Infertility 2%0.6RSV prophylaxis 4%1.5Rheumatoid arthritis 4%1.5Multiple sclerosis 4%1.5Transplant 5%1.6Hepatitis C 5%1.6Hemophilia 9%3.2Renal 10%3.4HIV/AIDS 36% $12.6Oncology Alignment – Specialty Pharmacy Specialty Market 2004 Billions Source: ESI Analysis Impact on Client Impact on Patient Impact on ESI Lower drug cost Lower co payment Higher profit/Rx Improved reporting Improved quality of care Higher client satisfaction Clients are Seeking Solutions for High-cost Specialty Drugs

14. 14 CuraScript Penetration into Express Scripts Retail CuraScript Mail 82% 73% 70% 69% 66% 2% 13% 17% 20% 25% 16% 14% 13% 11% 9% 100 90 80 70 60 50 40 30 20 10 0 Q1 2004Q2 2004Q3 2004Q4 2004Q1 2005 CuraScript Continues to Capture an Increased Share of Our Client’s Specialty Spend Percentage of Plan Costs

15. 15 What Are the Savings? Availability of Proven PBM Cost Management Tools Will Produce 20%–25% Savings (CBO) Paid by Cash Customer at Pharmacy Retail, Clinical. Formulary And Rebate Savings 24% Mail Savings 6% Paid by Express Scripts Clients Total Savings 30% COSTCOST Retail Pharmacy Cash Price Express Scripts Client Savings Express Scripts Client Costs

16. 16 Alignment – A Win-Win-Win Proposition Retail Non-pref. Brand Retail Pref. Brand Generics Mail Pharmacy Increased Savings Opportunities: Client Member Increased Profit Opportunities: Express Scripts Moving to preferred brands, mail and generics We make money by saving clients and members money Moving to preferred brands, mail and generics

17. 17 PBM’s Are Part of the Solution for Medicare Average Annual Drug Spend Among Medicare Population Source: Actuarial Research Corporation The Medicare Prescription Drug Act will shape the direction of our industry for years to come ESI is well positioned for 2006 Our 2006 offensive strategy is to help our managed care and carrier clients profitably grow their MA-PDs and PDPs We are building the foundation for 2007

18. 18 Benefits of ePrescribing Prescription & Pharmacy Benefit Information Point of Sale Point of CareBenefit / Gain Clinical Messages at pharmacy Physicians see clinical issues Better informed, safer prescribing Formulary Enforcement after prescribing Awareness at prescribing Better choices, increased generics Benefit Referenced at pharmacy Real-time guidance Cost-effectiveness, fewer callbacks Medication HistoryPartially known History while prescribingPatient safety Prescription Carried, faxed, called, mailed Convenience at pharmacy More efficient, patient safety Medicare Part D Will Advance Important Initiatives Including e- Prescribing

19. 19 We Deliver Against Client and Patient Expectations: To make the use of prescription drugs safer and more affordable

20. 20 Client/Patient Focus By membership Health Plan Sponsors Recognize Express Scripts Single Focus on Making Prescription Drugs More Affordable Why Express Scripts? Alignment With Clients Generics Specialty

21. 21 2006 Upsell Pipeline is Strong Significant potential to continue to manage client trends in key product categories New products continue to be developed and rolled out Strong track record of success 10,000 ( '000 Lives) 0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000 Home Delivery Generic Enforcement Narrowing Formularies New Clinical Products Specialty/CuraScript Three Tier Sold Weighted Pipeline

22. 22 Client Satisfaction Steadily Improving Service and satisfaction metrics have increased consistently quarter over quarter since 2003 with an early spike in 2005 Exceed 60% 65% 70% 75% 80% 85% 90% 95% 100% ESI Performance Expectations Likelihood to Recommend Likelihood to Renew 2003 2004 1q05

23. 23 Our Financial Results Express Scripts has demonstrated a proven track record

24. 24 Financial Overview 1Q EPS $1.14 — up 28% from last year Cash flow from operations of $138.1 million versus $97.8 million last year Record adjusted claims of 142 million, up 16% from last year Record generic utilization of 54% versus 49% last year Gross profit per adjusted claim of $1.87 versus $1.77 last year (excluding non- recurring gain last year) Increased 2005 EPS guidance Q1 2005 Highlights

25. 25 Financial Overview (1)Reflects a $70-$75 million reduction in Q2 2003 due to one-time impact of implementing a new wholesale purchase agreement (2)Excludes a $0.10 per share charge for the early retirement of debt (3)Excludes a $0.20 charge to increase legal reserves for the cost of defense. Quality of Earnings (1) (2) * Reflects a 12-month moving average of free cash flow (cash from operations less CapX) (3)

26. 26 Components of EPS Growth — 2004 * Excluding $25 million charge to increase legal reserves for the cost of defense and $5.5 million termination payment received 6% 7% 8%

27. Financial Overview EBITDA* per adjusted claim * A reconciliation of EBITDA to net income and to net cash provided by operating activities can be found in the Investor Relations section of Express Scripts’ Web site, www.express-scripts.com under Presentations. ** Excluding $25 million charge to increase legal reserves for the cost of defense and $5.5 million termination payment received. Pricing can be lowered as clients tighten formulary compliance, increase home delivery, utilize generics and restrict retail networks. These changes result in lower prices to our clients and greater profits to Express Scripts. 10.5% CAGR

28. 28 Gross Profit/SGA/EBITDA per Adj. Rx Future EBITDA per Adj. Rx Must Come From Gross Profit per Adj. Rx * Excluding $25 million charge to increase legal reserves for the cost of defense and $5.5 million termination payment received.

29. 29 Focus on Return on Invested Capital (ROIC) ROIC is our Preferred Performance Metric * Reflects operating income less tax divided by average invested capital, which consists of stockholder’s equity, plus interest bearing liabilities plus long-term deferred income taxes, net. ** Excludes $25 million charge to increase legal reserves for the cost of defense and 5.5 million termination payment received

30. 30 W hy Express Scripts? Industry-Leading ROIC We Lead Our Peer Group in ROIC Performance Source: Express Scripts Analysis

31. 31 Our Financial Goals 15% + EBITDA growth Increase gross profit per claim Maintain ROIC leadership 5%-7% 14%-16%

32. 32 Our Value Proposition Will Continue to Drive Growth Making the use of drugs safer and more affordable is more important than ever Plan sponsors will increasingly deploy our tools Express Scripts is well-positioned for sustainable growth Strong market fundamentals/new business opportunities Increased use of home delivery and generic drugs Growth in management of specialty pharmacy Productivity and capital structure improvements We have taken a different approach Alignment -- we make money by saving our clients money Strategic acquisitions have enhanced our value proposition