Etoposide (VP16) levels were determined by high-performance liquid chromatography assay in plasma, urine and surgical specimens of patients with choriocarcinoma undergoing surgery after a dose of 100 or 200 mg/m2 given as a 1-h infusion. The drug disappeared from plasma biexponentially, with a terminal half-life of 4.1 .+-. 0.4 h an apparent vol of distribution of 9 .+-. 1.1 l/m2, and clearance of 21.5 .+-. 3.1 ml/min per m2. Fifty and 740 min after the end of VP16 infusion, the drug concentrations in myometrial carcinoma or in normal myometrium were .apprx. 40-50% of those in plasma; 25-180 min after the end of drug infusion, the concentrations of VP16 in lung metastases amounted to 19-43% of those in plasma; in normal lung, the concentrations of VP16 were 38-61% of those in plasma. In subcutaneous tissue, VP16 levels were much lower than in plasma (.apprx. 5-27%). About 50% of VP16 was eliminated in the urine as unchanged drug, glucuronide or sulfate.