Treatment of patients with metastatic renal cell cancer (RCC) with interferon-alpha-2a (IFN) and 13-cis-retinoic acid (CRA) was first reported to be tolerable on an outpatient basis and to yield a 30% objective response rate. We sought to confirm these preliminary results by conducting a phase II trial of therapy with IFN/CRA in patients with bidimensionally measurable RCC. Twenty-five patients were enrolled. The median age was 58 (range, 47-75 years) and the median Karnofsky performance status was 90 (range 60-100). Seventeen patients (60%) had undergone prior nephrectomy and none had received prior systemic therapy. Treatment consisted of oral CRA at 1 mg/kg/day and IFN self-administered by subcutaneous injection at 3 MU/day with weekly escalation to 6 and 9 MU/day. Treatment was well tolerated, with cheilitis, influenza-like symptoms, and fatigue the most common toxicities. Severe toxicity was reversible and consisted of grade 4 cheilitis in one patient and grade 3 malaise/fatigue in two patients. One complete and four partial responses were observed, for an objective response rate of 20% (95% confidence interval, 4-36%). We conclude that treatment with CRA/IFN for RCC is tolerable on an outpatient basis and induces objective responses in some patients. The contribution, if any, of CRA to the responses observed will be determined in ongoing randomized phase III trials.