We have conducted a broad phase II clinical trial of chlorozotocin in 74 patients including 28 with malignant melanoma, 18 with breast cancer, nine with non-Hodgkin's lymphoma, six with nonseminomatous testicular cancer, five with ovarian cancer, four with sarcoma, three with non-beta islet cell carcinoma of the pancreas, and one with anaplastic carcinoma of the thyroid. Objective responses were noted only in 15% of the patients with melanoma and in 11% of the patients with non-Hodgkin's lymphoma. Significant leukopenia and thrombocytopenia were observed only in previously treated patients. Chlorozotocin does not appear to offer clinically significant advantages over other currently available nitrosoureas.