Plasma pharmacokinetics of VP16-213 were investigated after a 30-60 min infusion in 14 adult patients and six children. In adult the elimination half-life (T1/2 beta), plasma clearance (Clp) and volume of distribution (Vd) were respectively 7.05 +/- 0.67 h, 26.8 +1- 2.4 ml/min/m2, and 15.7 +1- 1.8 l/m2; in children 3.37 +/- 0.5 h, 39.34 +1- 6.6 ml/min m2, and 9.97 +/- 3.7 l/m2. After repeated daily doses no accumulation of VP16-213 was found in plasma. The unchanged drug found in the 24 h urine after administration amounted to 20-30% of the dose. In eight choriocarcinoma patients plasma levels of VP16-213 were measured after oral capsules and drinkable ampoules. The bioavailability compared to the i.v. route was variable, mean values being 57% for capsules and 91% for ampoules. In one further patient, with abnormal d-Xylose absorption results, VP16-213 was not detectable in plasma after the oral ampoule dose. Steady state levels investigated in three patients after 72 h continuous VP16-213 infusion (100 mg/m2/24h) were around 2-5 micrograms/ml. Levels of VP16-213 were undetectable in CSF after i.v. or oral administration.