OBJECTIVES: To examine access to and use of HIV highly active antiretroviral therapy (HAART) by race/ethnicity in Medicaid and the AIDS Drug Assistance Program (ADAP) in 1998 in four states. METHODS: The authors analyzed reimbursement claims and AIDS surveillance data in California, Florida, New York, and Texas. Study subjects were identified using diagnostic or medication codes specific to HIV. The race/ethnicity of program enrollees was compared to representation in the HIV epidemic to examine access. Claims for antiretroviral (ARV) use were compared to U.S. Public Health Service treatment guidelines to assess HAART use. RESULTS: The authors identified 151,000 HIV-infected individuals in these two programs in the four states. Evidence of AIDS or symptomatic HIV was present in 78%-88% of enrollees in Medicaid, versus 31%-48% in ADAP. African Americans participated in Medicaid 10%-53% above and in ADAP 17%-31% below representation in the epidemic. Non-Latino whites exhibited the opposite pattern, being in Medicaid 5%-38% below and in ADAP 9%-65% above epidemic representation. Latinos participated more in ADAP (7%-31%), except in New York. HAART use over 90 days (July-September) ranged from 38% to 76% by program and state. Differences by race/ethnicity were inconsistent and small: African Americans had lower HAART use by 6%-14% in California and Florida Medicaid, and Latinos had higher HAART use by 2%-11% in ADAP and in Texas Medicaid. CONCLUSIONS: African Americans were more likely to access HIV drugs through Medicaid than through ADAP, which may reflect differences in program eligibility criteria as well as care seeking later in HIV disease. Differences in the use of HAART by race/ethnicity within state programs were small.