KW-2189, a semisynthetic duocarmycine antibiotic has been shown to exert antiproliferative effects against human tumor cell lines in vitro and animal tumor models in vivo. Phase I studies identified myelosuppression as the most noteworthy adverse effect. Presented are two concurrent phase II studies assessing the antitumor and toxicity profile of KW-2189 in metastatic melanoma patients. One of the studies accrued patients with a history of prior melanoma therapy and the other accrued patients without a history of prior melanoma therapy. KW-2189 was administered at 0.4 mg/m2 to previously treated patients and 0.5 mg/m2 to the previously untreated. Treatment was administered intravenously on day 1 of a 6-week cycle. Thirty previously untreated and 15 previously treated patients were accrued. The toxicity profiles of the both groups of patients were similar. Of the 15 previously treated patients, 8 completed once cycle of treatment, 2 completed 2 cycles, and 5 completed 3 cycles. Dose modification for neutropenia/ thrombocytopenia was necessary in six patients. Among the previously untreated cohort (30 patients), 16 completed 1 cycle, 5 completed 2 cycles, 4 completed 3 cycles, 3 completed 4 cycles, and 2 completed 6 cycles. Doses were modified (neutropenia or thrombocytopenia) in 11 patients. None of the 15 previously treated patients responded to therapy. Four patients remained stable during two cycles. Five of the previously untreated patients achieved a partial remission/regression. Response duration ranged from 2.8 to 16.6 months. Overall objective response rate was 17%. Regarding survival, one previously treated patient is still alive 2.9 years after study entry, and three previously untreated patients are still alive 1.6, 2.3, and 2.9 years after study entry. The 1-year survival rate for previously treated patients is 27% and for the untreated patients is 23%. In summary, the lack of significant antitumor activity of KW-2189 and its associated toxicity suggest that further testing of this regimen in patients with stage IV melanoma is not warranted.