A total of 15 patients with relapsed Wilms' tumor were treated with carboplatin as a single agent. There were six females and nine males, aged between 2 and 9 years (me-dian:5). The treatment consisted of carboplatin given I.V. as a single agent at a dose of 550 mg/m2 over 1 hour every 3 weeks. There were four (26%) complete responses, four (26%) partial responses, one stable disease, and six with progressive disease. In all patients a total of 56 courses were given and the toxicities found were leukopenia and thrombocytopenia. The overall response rate was encouraging and the toxicity was acceptable and reversible. © 1994 Wiley-Liss, Inc.