Following recent reports suggesting that the addition of cimetidine to interferon may enhance response rates in patients with metastatic malignant melanoma, we have completed a Phase II study of the use of recombinant alpha 2 interferon and cimetidine in patients with advanced malignant melanoma and who had progressive disease following interferon therapy alone. We observed two partial responses, no complete responses, and two patients had stable disease. Toxicity encountered was analogous to that of interferon alone. We conclude that the additional of cimetidine to alpha interferon is not beneficial in the treatment of advanced metastatic malignant melanoma.