A pharmacokinetics study was performed in HIV-infected patients who used indinavir/ritonavir (800/100 mg twice a day) plus efavirenz in the European and South American Study of Indinavir, Efavirenz and Ritonavir. Indinavir plasma concentrations were similar to values previously obtained in healthy volunteers who used the same combination. Efavirenz concentrations were higher than reported before. The pharmacokinetic data suggest that indinavir/ritonavir plus efavirenz (without dose modifications) should be effective in treatment-naive patients, and this was supported by the treatment response of the participants.