In patients with metastatic renal cell carcinoma response rates of 7–26% have been achieved with immunotherapy. A high response rate of 48% in 35 patients has been reported for treatment with the combination of interferon-α (IFN-α), interleukin-2 (IL-2) and 5-fluorouracil (5-FU) (Atzpodien et al (1993 a) Eur J Cancer29A: S6–8). We conducted a multicentre phase II study to confirm these results. Metastatic renal cell carcinoma patients were treated as outpatients with an 8-week treatment cycle. Recombinant human IL-2 20 MU m−2was administered subcutaneously (s.c.) three times a week (t.i.w) in weeks 1 and 4 and 5 MU m−2t.i.w. in weeks 2 and 3. Recombinant human IFN-α 2a 6 MU m−2was administered s.c. once in weeks 1 and 4 and t.i.w. in weeks 2 and 3, and 9 MU m−2t.i.w. in weeks 5–8. 5-FU (750 mg m−2) was given as a bolus injection intravenous once a week in weeks 5–8. The treatment cycle was repeated once in case of response or minor response. Fifty-two patients entered the study. All had undergone a nephrectomy and had progressive metastatic disease. The median WHO-performance status was 1, the median number of metastatic sites was 2 (range 1–5) and the median time between the diagnosis of the primary tumour and the start of treatment was 12.9 months (range 1–153). Among the 51 patients, including four patients with early progressive disease, who were evaluable for response, the response rate was 11.8% (95% confidence interval (CI) 2.9–20.7%), with no complete responses. Median duration of response was 8.3 (range 3.8–22.4+) months. Median survival was 16.5 (range 1.8–30.5+) months. Grade 3/4 toxicity (WHO) occurred in 29/52 (55.8%) of the patients in cycle 1 and in 6/16 (37.5%) of the patients in cycle 2. It consisted mainly of anorexia, fatigue, nausea, fever and leucocytopenia. We cannot confirm the high response rate in patients with metastatic renal cell carcinoma treated with the combination of IFN-α, IL-2 and 5-FU, as described by Atzpodien et al. © 2000 Cancer Research Campaign