The new semisynthetic epipodophyllotoxin VP 16-213 has been tested for antitumor activity and toxicity in a non-randomized phase II trial. The study included 33 patients with solid tumors and acute leukemias. The drug was given in 5-day courses every 3 weeks, parenterally for the first 2 courses and thereafter orally. Subjectively VP 16-213 was well tolerated in both i.v. and oral administration, but almost universally induced leukothrombopenia and hair loss. The best results were achieved in 12 patients with oat cell carcinoma of the lung (4 good and 4 less good responses). Remissions of lesser quality were also observed in anaplastic lung cancer, ovarian carcinoma and acute myelomonocytic leukemia. VP 16-213 possesses proven, clinically valuable cytostatic activity against various human neoplasms. Complementary studies to establish its optimum dosage and administration, and its place in combination chemotherapy, are in progress.