Liblomycin (NK313) is a bleomycin analog that has proved to be associated with less pulmonary toxicity and with more potent antitumor activity than bleomycin in animal tumors. In a phase I study, pulmonary toxicity was not observed, whereas myelosuppression was the dose-limiting factor. The maximum tolerated dose was 140 mg/m2 given once a week for 4 weeks. In the present phase II study, patients with malignant lymphomas received liblomycin at 80 or 100 mg/m2 by intravenous infusion over 15 min once a week for 4 weeks. A total of 39 patients were entered, and 31 [4 with Hodgkin's disease (HD) and 27 with non-Hodgkin's lymphoma (NHL)] were evaluable. The median age of the patients was 52 years (range, 22-74 years), and their performance status ranged from 0 to 3. In all, 28 of the patients had a history of intensive anticancer chemotherapy. Responses were evaluated according to WHO criteria. We obtained 1 complete remission and 9 partial remissions (PRs), for an overall response rate of 37%, in the 27 patients with NHL, whereas 1 PR was achieved in the 4 patients with HD. In all, 9 PRs (32.1%) were obtained in patients who had been exposed to prior chemotherapy, including 4 PRs (33.3%) in 12 patients who had previously been treated with bleomycin. Myelosuppression and nausea and vomiting were the major toxicities, which occurred in about 50% of the patients, and myelosuppression was severe in two patients treated at a dose of 100 mg/m2. We concluded that liblomycin demonstrated significant antitumor activity against malignant lymphomas.