We applied haemodialysis to clear platinum (Pt) circulating species following renal insufficiency due to an accidental cisplatin overdosage (205 mg/m2 instead of 100 mg/m2). Serum samples were repeatedly obtained during this clinical episode from day 5 up to day 30 after cisplatin dosing. A serum aliquot taken at day 22 after cisplatin administration was tested to assess the possible cytotoxicity exhibited by the circulating Pt species on a head and neck tumour cell line. The profile of ultrafiltrable (UF) Pt during successive haemodialysis cycles was striking. After each haemodialysis cycle, a marked decrease in UF Pt, occurred but was followed by more or less pronounced rebounds. Cisplatin concentration-cytotoxic effect curves obtained in vitro from patient serum before cisplatin administration and healthy control serum exhibited very similar concentration effect profiles. In contrast, the patient serum taken at day 22 after cisplatin administration resulted in marked cytotoxic effects, which were much greater than those which could have been anticipated considering the Pt concentration of this serum sample. The present report underlines the limited usefulness of haemodialysis for rescuing cisplatin treated patients, exhibiting unanticipated postinfusion renal failure with overexposure to the drug. The in vitro investigations suggest that pharmacological effects of Pt derivatives may not only be attributable to short-term effects of the drug diffusion into tissues, but also to more delayed effects from Pt circulating species.