Human leukocyte interferon (IFN alpha) was administered to 15 patients with epithelial ovarian carcinoma after previous chemotherapy or therapeutic irradiation. One objective response was observed. Three patients had possible stable disease for up to 6 months, including two patients who were re-explored 6 months after commencing IFN alpha and one patient who was observed to have a less than 50% reduction in her tumor diameters. Three of seven patients demonstrated clinical responses to subsequent chemotherapy, indicating an absence of resistance to subsequent chemotherapy. Toxicity included the relatively mild symptoms of anorexia, lassitude, and diarrhea. Malabsorption was observed in one patient. Platelet depression and abnormal enzyme liver functions were also observed more frequently following IFN alpha. No life-threatening toxicity was observed.