Piperazinedione given iv once every 3-4 weeks at a starting dose of 9-12 mg/m2 (4.5-12 mg/m2 for patients with myeloma) was evaluated in a Southwest Oncology Group phase II study for patients with far-advanced refractory lymphoma or multiple myeloma. Among 36 patients fully evaluable for tumor response (adequate trial), partial responses were observed in five (71%) of seven patients with Hodgkin's disease, in three (19%) of 16 patients with non-Hodgkin's lymphoma, and in none of 13 patients with multiple myeloma. Response was observed by the time of the second (five patients) or third (three patients) course. The median duration of response was 3.7 months (range, 1-17+ months). The dose-limiting toxic effects were hematologic, with 18 (50%) of 36 patients evaluable for toxicity experiencing severe leukopenia (wbc count less than 2000/mm3) and 22 (61%) experiencing severe thrombocytopenia (platelet count less than 50,000/mm3). Twenty patients had a decrease from their pretreatment hemoglobin level of greater than or equal to 2 g/100 ml. Hematologic toxic effects were often unpredictable and in several patients quite prolonged. This study indicates that piperazinedione had definite antitumor activity in patients with Hodgkin's disease and further trials in this disease using the drug at a reduced dose in combination with other effective drugs appear warranted.