Twenty-two patients with cutaneous metastases of malignant melanoma were treated with intralesional injections of the methanol extraction residue of bacillus Calmette-Guerin (MER). The local reaction consisted of erythema and pustule formation followed by ulceration and tumor necrosis. Side effects included fever, chills, headache and malaise in the majority of patients; nausea, vomiting, cyanosis and hypotension occurred infrequently. Hypersensitivity reactions were not observed. Temporary abnormalities in liver function were seen in 11 of 19 patients tested. Reversible lymphopenia and thrombocytopenia developed in 7 of 17 and 7 of 18 patients, respectively. Immune function, as measured by skin tests for delayed hypersensitivity and the in vitro response of isolated lymphocytes to mitogens and microbial antigens, was not influenced by treatment with MER. Transient increases were observed in total hemolytic complement, complement components and the reduction of nitroblue-tetrazolium by neutrophils. Eight of eighteen evaluable patients showed a complete disappearance of all injected lesions. We conclude that intratumoral injection of MER is effective treatment for cutaneous metastases of malignant melanoma, with a complete response rate comparable to that observed after intralesional injection of BCG.