OBJECTIVES: Both angiotensin-converting-enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) have been widely used for treatment of hypertension, heart failure, diabetes mellitus and kidney disease. The purposes of this study were to describe the utilization, price and expenditure trends of ACEIs and ARBs and to assess market-share competition between ACEIs and ARBs.   METHODS: A retrospective, descriptive time-series analysis was performed using the National Medicaid pharmacy claims database from 1991 to 2008. The quarterly prescription numbers and reimbursement amounts were calculated over time by summing data for individual drug products. The quarterly per-prescription reimbursement as a proxy for drug price was computed for all brands and generics of ACEIs and ARBs. The market shares were calculated based on both prescription numbers and Medicaid payments. RESULTS: The ACEI prescriptions increased from 4.8 million in 1991 to 16.5 million in 2004, then dropped to 2.3 million in 2008. Meanwhile, ARB prescriptions increased from 0.03 million in 1995 to 7.5 million in 2004, then dropped to 2.1 million in 2008. Concurrently, annual expenditure for ACEIs increased from $179 million in 1991 to $593 million in 2002, and dropped to $64 million in 2008. Expenditure for ARBs  increased from $1.3 million in 1995 to $515 million in 2005, and dropped to $174 million in 2008.  Market shares for generic ACEIs like captopril, lisinopril and enalapril increased rapidly. All brand-name prices for ARBs and ACEIs increased over time regardless of new branded or generic drug entry, while generic prices decreased over time. CONCLUSIONS: Dramatically increased utilization of both ACEIs and ARBs may be due to their wide therapeutic indications and efficacy. A significant drop in utilization from 2006-2008 was related to the introduction of Medicare Part D.  Increased utilization of generic ACEIs was likely due to the Medicaid generic substitution policy and changes in prescribing patterns.