A simple high-performance liquid chromatography method for the determination of the human immunodeficiency virus protease inhibitor atazanavir in human plasma samples was developed and validated. The method involved a rapid and simple solid-phase extraction of atazanavir using Oasis HLB 1cc cartridges, an isocratic reversed-phase liquid chromatography on an XTerra RP18 (150mmx4.6mm, 3.5microm) column, and ultraviolet detection at 203nm. The mobile phase consisted of phosphate buffer (pH 6, 52.5mM) and acetonitrile (43:57, v/v). Up to 48 samples could be measured in one day since the run-time of one sample was 30min. The assay was linear from 0.04 to 10microg/ml with a lower limit of quantification of 0.04microg/ml. The mean absolute recovery of ATV was 98.1%. The method was precise, with both intra-day and inter-day coefficients of variation < or =3.0%, and accurate (deviations ranged from -3.0% to 4.5% and from -3.6% to 4.7% for intra-day and inter-day analysis, respectively). There was no interference from 35 tested potentially co-administrated drugs. This method provides a simple, sensitive, precise and reproducible assay for the therapeutic drug monitoring of atazanavir in clinical routine of laboratories with standard equipment.