Mitomycin is a cytotoxic antibiotic that was first introduced into clinical use in 1958. Not until twenty years later was it recognised that haemolytic uremic syndrome could develop after treatment with mitomycin. It can be asked whether this condition was undiagnosed in previous years, since its frequency is now reported to be 4-15%. The disease appears to be dose-related, since it rarely occurs in patients who have received mitomycin < 30 mg/m2. No effective therapy has been established. We describe two patients with breast cancer in remission after treatment with mitomycin in combination with 5-fluorouracil. Both developed haemolytic uremic syndrome with fatal outcome.