Ifosfamide is an alkylating agent which has been incorporated into frontline therapy for a number of malignant paediatric tumours. Recent data appears to suggest that tubular dysfunction may result from incorporation of this drug into chemotherapy schedules and that toxicity may be dose related. A detailed investigation of renal function was performed in a group of patients, ranging in age from 8 months to 15.9 years (median 8.6 years) with rhabdomyosarcoma (n = 11) and Ewing's sarcoma (n = 9) who were currently receiving (n = 4) or had completed ifosfamide (n = 16) therapy a mean of 16 months at the time of study. All but one patient demonstrated some degree of renal dysfunction and toxicity did not necessarily appear to be dose related. Implications for incorporation of this agent into future schedules for childhood sarcomas, which can expect to cure more than 60% of such children, must be addressed. The importance of ongoing monitoring is emphasised.