Purpose: The purpose of this research was to determine the toxicity and immunological activity of large multivalent immunogen (LMI), a preparation of tumor cell membranes affixed to amorphous silica microbeads, in patients with melanoma. Experimental Design: Nineteen patients with metastatic (stage IV) melanoma were entered into the study, of whom 15 received the full 3 months of treatment with LMI. LMI was administered without adjuvant, one-half intradermally (i.d.) and the other half s.c. Because we expected little toxicity, we first treated 2 patients at each dose level, 10-, 30-, or 100-million tumor cell equivalents on weeks 0, 4, and 8, and subsequently randomized the remaining 13 patients to receive treatment with one of those dosage schedules, for a total of 19 patients. Two patients who were registered were found to be ineligible because of brain metastases, and 2 others did not complete the course of treatment for reasons other than toxicity. Thus, 15 patients were fully evaluable. Patients with evidence of a clinical response (at least stable disease at the 12-week checkpoint) had the option of continuing treatment at 4-week intervals. Frequencies of cytolytic T cell precursors against HLA-A2 matched melanoma cells, and delayed-type hypersensitivity to a melanoma cell membrane preparation from a component melanoma cell line were performed to measure immunological efficacy, and serum chemistries and complete blood counts were performed every 2 weeks throughout the study to measure possible toxicity. Computed tomography scans were performed pretreatment and at week 12 to measure possible beneficial effects on known lesions. Results: Eight of the 15 evaluable patients had an increase in cytolytic T-cell precursors during the course of therapy, usually by day 42. No patient had demonstrable delayed-type hypersensitivity to a melanoma membrane preparation before or after treatment. No toxicity of any kind was observed. A degree of clinical effectiveness of LMI was suggested by the elicitation of stable disease in 5 patients at 12 weeks. One patient had >50% regression of a lung nodule but progression of disease to the brain, whereas a second patient had a bona fide partial remission of a 3-cm diameter solitary lung nodule. Conclusions: LMI was nontoxic, improved immunological reactivity to melanoma cells, and showed evidence of clinical effectiveness (shrinkage of tumor) in 1 patient. Additional studies with LMI with added adjuvant materials, in melanoma and other cancers, appear warranted.