Previous clinical investigations using interferons (IFNs) have shown activity against epithelial ovarian cancer. The objective of this study was to determine the maximum tolerated dose of intraperitoneal (ip) IFN-alpha 2b which could be administered in combination with intravenous (iv) cis-platinum plus cyclophosphamide chemotherapy. After comprehensive surgical staging and maximal cytoreduction, previously untreated patients with primary ovarian adenocarcinoma were entered at one of five IFN dose levels. IFN-alpha 2b (5-30 x 10(6) units) was administered ip on Day 1 (+/- Day 8). cis-Platinum (75 mg/m2) plus cyclophosphamide (750 mg/m2) were administered iv on Day 2 with prophylactic hydration and anti-emetics. Courses were repeated every 3 weeks for 8 cycles. Adverse effects were recorded using standard Gynecologic Oncology Group toxicity scales. Fifteen patients with mean age 56 years (range 43-73) were entered and received a combined total of 100 treatment cycles. Catheter-related complications occurred in 8 patients, and in three cases lead to catheter removal and discontinuation of ip therapy. Two patients experienced grade 2-3 nephrotoxicity and 1 experienced grade 2 peripheral neuropathy. There was a single episode of chemical peritonitis. Myelosuppression was the dose-limiting toxicity with grade 3-4 leukopenia complicating 6, 5, 12, 11, and 17 cycles at dose levels 1-5, respectively. No patient completed planned treatment without interruption or dose reduction. Planned cis-platinum dose intensity was most compromised at the fifth IFN-alpha 2b dose level. The maximum tolerated dose of IFN-alpha 2b was determined to be 20 x 10(6) units repeated on Days 1 and 8 of this 21-day cis-platinum plus cyclophosphamide chemotherapy cycle.