A randomized prospective therapy trial in patients with stage III optimal epithelial carcinoma of the ovary was accomplished by the Gynecologic Oncology Group. Therapy with melphalan or melphalan plus immuno-adjuvant, Corynebacterium parvum (C. parvum), was utilized as adjuvant treatment following surgical therapy. One hundred eight-five patients were eligible for evaluation with 87 patients in the melphalan group and 98 patients in the melphalan plus C. parvum group. The comparison of the treatment regimens showed no differences with respect to either progression-free interval or survival. However, it should be noted that a 50% 3-year survival was obtained. A group was identified, using four prognostic factors that had 80% survival at 3 years. Maximum size of the residual tumor, as well as performance status, was not prognostically significant. This study demonstrates a lack of efficacy of the addition of C. parvum to melphalan for this patient population.