Ifosfamide is an alkylating agent used in the treatment of a variety of solid tumours. Ten to 15% of patients treated with ifosfamide develop an encephalopathy. Methylene blue (MB) may be used in the treatment of this encephalopathy. The purpose of this study was to evaluate the neuroprotective effect of MB in these patients and to review the literature. Between 1993 and 1997, 52 patients (age 16-77 years) with solid tumours were treated with ifosfamide in dosages ranging from 3 to 5 g m(-2) q3w when given in combination schedules and up to 12 g m(-2) q4w when given as a single agent. Twelve patients developed central nervous system (CNS) depression, defined as National Cancer Institute Common Toxicity Criteria (NCI-CTC) neurocortical toxicity grade 2 or higher. Eight were treated with MB at a dose of 6 x 50 mg day(-1) intravenously (i.v.). Four recovered fully within 24 h, two recovered partially after 24 h and completely after 48 h while two recovered only after 72 h. Four patients did not receive MB and all recovered only after 48 h. Three patients received prophylaxis with MB at a dose of 4 x 50 mg day(-1) i.v. for the subsequent chemotherapy cycles. Two developed milder encephalopathy; one had no CNS depression at all. We conclude that MB is an effective treatment for ifosfamide-induced encephalopathy. Our findings suggest that it may also be used as a prophylactic agent.