A simple method for the simultaneous determination of zidovudine and nevirapine in human plasma by reversed-phase liquid chromatography with UV detection at 265 nm was developed. A solid-liquid extraction procedure with internal standard was applied to the samples prior to analysis. The system requires a Zorbax SB-C18 column, 250 x 4.6 mm I.D. and a mobile phase composed of potassium dihydrogen phosphate (10 mM; pH 6.5)-acetonitrile (83:17, v/v). Peak-areas are linear; correlation coefficients are better than 0.999; both inter- and intra-day accuracy and precision are lower than 15%. Extraction recoveries are higher than 90% for both zidovudine and nevirapine. The method proposed was employed to determine the levels of the two retroviral drugs in plasma from HIV infected human subjects.