We describe the case of a 35-year old male who developed acute renal failure following high dose methotrexate therapy for Burkitt's non Hodgkin lymphoma. Serum methotrexate levels reached 37 micromol/l, and remained higher than 1 micromol/l for more than a week. Folinic acid rescue was intensified to 200-400 mg intravenously every 4 hours. As methotrexate binds markedly to proteins, plasma exchange was initially chosen, 4 sessions being performed from day 2 to day 4. The methotrexate pharmacokinetic profile was not significantly modified during plasma exchange, and serum drug level was 3 micromol/l. Continuous veno-venous hemodiafiltration was therefore performed from day 5 to day 10. This procedure also seemed ineffective, with evidence of low ultrafiltrate clearance. No extrarenal toxicity was observed in our patient. Thus, conventional extrarenal procedures appear to have a limited role in the setting of overexposure to methotrexate. The use of very high doses of folinic acid in our case probably played a major role in the eventual favorable outcome.