Adult AIDS Clinical Trials Group (AACTG) Protocol 886 examined the dispositions of indinavir, efavirenz, and abacavir in human immunodeficiency virus-infected subjects who received indinavir at 1,000 mg every 8 h (q8h) and efavirenz at 600 mg q24h or indinavir at 1,200 mg and efavirenz at 300 mg q12h with or without abacavir 300 at mg q12h. Thirty-six subjects participated. The median minimum concentration in plasma (Cmin) for indinavir administered at 1,200 mg q12h was 88.1 nM (interquartile range [IR], 61.7 to 116.5 nM), whereas the median Cmin for indinavir administered at 1,000 mg q8h was 139.3 nM (IR, 68.8 to 308.7 nM) (P = 0.19). Compared to the minimum Cmin range for wild-type virus (80 to 120 ng/ml) estimated by the AACTG Adult Pharmacology Committee, the Cmin for indinavir administered at 1,200 mg q12h (54 ng/ml) is inadequate. The apparent oral clearance (CL/F) (P = 0.28), apparent volume of distribution at steady state (Vss/F) (P = 0.25), and half-life (t1/2) (P = 0.80) of indinavir did not differ between regimens. The levels of efavirenz exposure were similar between regimens. For efavirenz administered at 600 mg q24h and 300 mg q12h, the median maximum concentrations in plasma (Cmaxs) were 8,968 nM (IR, 5,784 to 11,768 nM) and 8,317 nM (6,587 to 10,239 nM), respectively (P = 0.66), and the Cmins were 4,289 nM (IR, 2,462 to 5,904 nM) and 4,757 nM (IR, 3,088 to 6,644 nM), respectively (P = 0.29). Efavirenz pharmacokinetic parameters such as CL/F (P = 0.62), Vss/F (P = 0.33), and t1/2 (P = 0.37) were similar regardless of the dosing regimen. The median Cmax, Cmin, CL/F, Vss/F, and t1/2 for abacavir were 6,852 nM (IR, 5,702 to 7,532), 21.0 nM (IR, 21.0 to 87.5), 43.7 liters/h (IR, 37.9 to 55.2), 153.9 liters (IR, 79.6 to 164.4), and 2.0 h (IR, 1.8 to 2.8), respectively. In summary, when indinavir was given with efavirenz, the trough concentration of indinavir after administration of 1,200 mg q12h was inadequate. Abacavir did not influence the pharmacokinetics or exposure parameters of either indinavir or efavirenz. The levels of efavirenz exposure were similar in subjects receiving efavirenz q12h or q24h.