OBJECTIVES Angiotensin-converting-enzyme (ACE) inhibitors have been widely used for treatment of hypertension, heart failure, diabetes mellitus and kidney disease. The purposes of this study was to describe the utilization and spending trends of ACE inhibitors and assess market-share competition between brand-name and generic drugs in the US Medicaid Program. METHODS Since captopril, the 1st ACE inhibitor, introduced in 1981, there are 22 brand-names including 10 combination drugs are available in the market. Multiple generic ACE inhibitors are available including benazepril, captopril, enalapril, fosinpril, lisinopril, moexipril, perindopril, quinapril, and ramipril. National Medicaid pharmacy data were extracted from CMS from 1st quarter 1991 to 3rd quarter 2007 in order to obtain quarterly total prescription numbers and reimbursement amounts. The per-prescription reimbursement as a proxy of drug price was calculated for all study ACE inhibitors. The market-shares were calculated based on proportion of total prescriptions numbers. RESULTS By 2005, the expenditure for ACE inhibitors reached to $ 490.5 million ($248 million for brand drugs and $242.5 million generic drugs). But It had been seen a sudden drop on the utilization of both brand-name and generic ACEIs since 2006 quarter 1 because of implementation of Medicare PartD. The average per-prescription reimbursement for brand-name ACE inhibitors increased overtime from $35.2 in the first quarter of 1991 to $67.1 in the third quarter of 2007, whereas per-prescription reimbursement for generics decreased from $31.5 in 1996 to $22.4 in 2007. After the generics entry, the market share of brand-name drugs dropped from 100% in 1991 to 12.6% in 2007. CONCLUSIONS Generic reimbursement prices decreased due to their competitions, while the brand-name drug prices increased overtime regardless new entry counterparts. There is a dramatic competition in market share between brand-name and generic drugs in Medicaid program.