One hundred twenty patients with metastatic malignant melanoma were randomized to receive either cyclophosphamide, 600 mg/m2 IV, on day 1 plus DTIC 200 mg/m2 IV days 1 through 5, or the same chemotherapy plus C. parvum 5 mg/m2 IV on day 8 and day 15. Therapy was repeated every 21 days. Although responses were observed in 13.8% of patients on cyclophosphamide plus DTIC versus 25.5% of patients on cyclophosphamide plus DTIC plus C. parvum, the median duration of remission was 15.6 weeks on chemotherapy and 13.0 weeks on chemotherapy plus C. parvum. Furthermore, survival was similar on both regimens (6.1 months versus 5.7 months, respectively). Favorable prognostic factors included metastatic disease confined to skin or lymph nodes (33% responses), performance status greater than 70% (24% response rate), and administration of three or more courses of chemotherapy (31% response rate). The dose limiting toxicity was myelosuppression, which was equal on both regimens. Chills and fever were common in response to C. parvum, and, rarely hypotension, cyanosis, or immune nephritis was observed. The addition of C. parvum to chemotherapy with cyclophosphamide plus DTIC is not recommended.