Oral glucose tolerance tests were performed in 47 children with acute lymphoblastic leukemia (ALL), treated according to 2 consecutive protocols. Glucose and insulin values were assessed before and after L-asparaginase (L-asp). 30 children (group A) received L-asp as a single-agent consolidation course, after achieving remission with vincristine (VCR) and prednisone (PDN). Normal insulin and glucose levels were found in all patients before L-asp; 4 children (13%) had a transient impaired glucose tolerance (IGT) after completing L-asp therapy. 17 children (group B) were given L-asp during induction therapy with VCR and PDN, and all achieved complete remission. 5 patients (23%) had IGT, without hypoinsulinemia, before L-asp administration. IGT normalized in 4 patients after L-asp, the other children developed a diabetes mellitus. Only 1 patient, with a normal IGT test before L-asp therapy, showed a transient IGT after L-asp. In patients with ALL, the presence of IGT before treatment may be related to leukemia. The concomitant use of steroids does not influence the incidence of IGT in our series. Our data reveal normal insulinemia in patients with IGT. Thus, the leukemic process itself may play a much more significant role in inducing abnormalities in carbohydrate metabolism.