The renal toxicity of antitumoral drugs is an increasingly disturbing problem. These drugs are now prescribed in an ever wider variety of cases, and delayed renal reactions, previously unknown, are revealed by the longer survivals obtained. For a number of years, patients whose cancer had been cured have been placed under haemodialysis on account of drug-induced renal failure. The renal toxicity of cisplatinum, nitrosoureas and methotrexate is well-known, but mitomycin C is also capable of inducing permanent renal failure; the delayed toxicity of this drug explains that it has long been underestimated. This example emphasizes the need for close co-operation between oncologists, nephrologists and pharmacologists in order to determine, for each patient, the most effective treatment with the minimum of side effects.