Fifteen evaluable patients with metastatic malignant melanoma who had received no prior chemotherapy were treated with high-dose cimetidine orally, 600 mg q.i.d. Although three patients had stable disease lasting 2-4 months, there were no objective responses. Median survival was 5.3 months (range 1-18 months). Toxicity was essentially negligible except for severe diarrhea in one patient and worsening liver function abnormalities in another. High-dose cimetidine does not have any significant activity in metastatic melanoma.