The results of two randomized, single-dose, crossover bioavailability studies are presented which describe the pharmacokinetics and oral bioavailability of nevirapine, a novel nonnucleoside antiretroviral drug. In the first study 12 healthy male volunteers received nevirapine 15 mg via short-term i.v. infusion or orally as a 50 mg tablet or reference solution (50 mg/200 mL). Following the i.v. dose, nevirapine had a low systemic clearance (Mean +/- S.D., Cl = 1.4 +/- 0.3 L/h) and a prolonged elimination phase (t(1/2beta) = 52.8 +/- 14.8 h; MRT = 81.4 +/- 22.4 h). Nevirapine absolute bioavailability was 93 +/- 9% and 91 +/- 8% for the tablet and oral solution, respectively. In the second study, 24 healthy male volunteers were administered nevirapine as a 200 mg production-line tablet or oral reference solution (200 mg/200 mL). There was no significant difference in bioavailability between the tablet and reference solution. Overall, comparison of the pharmacokinetic parameters between the 50 and 200 mg doses indicates that nevirapine is well absorbed at clinically relevant doses. The absorption profiles using deconvolution revealed no evidence of differential enzyme induction between the two doses or routes of administration following a single dose.