In patients with small-cell lung cancer VP-16-213 is often given in combination with doxorubicin and cyclophosphamide. Little is known about possible interactions between these drugs. Therefore we investigated in 7 patients the pharmacokinetics of VP-16-213, with and without the other two drugs. We found no change in the pharmacokinetics. We also provide evidence that the pharmacokinetics did not change in two sequential administrations of the drug. Pharmacokinetic data are in agreement with previous reports.