Methotrexate (MTX) has been used in the treatment of childhood acute lymphoblastic leukemia (ALL) for over 40 years. A number of the acute toxicities are common with high dose methotrexate (HDMTX) infusion, including myelosuppression, vomiting, orointestinal mucositis, hepatic and renal toxicities, neurological disturbances. On the other hand, effect of HDMTX therapy on glucose metabolism was not known. Between 2001 and 2002, twenty children with acute lymphoblastic leukemia at the Dr. Sami Ulus Children's Hospital, Department of Pediatric Hematology and Oncology were treated according to the St. Jude ALL XIII protocol were eligible to this study. Dose of MTX (2 gr/m2) was infused over 24 hours. Orally glucose tolerance test was performed at before HDMTX therapy, 1 day and 1 week after the therapy. We found that HDMTX infusion did not significantly effect on orally glucose tolerance test during the first week.