Forty-five children with acute nonlymphoblastic leukemia in relapse received a total of 56 courses of L-asparaginase combined with vincristine and prednisone. The complete remission rate of 40% (12 of 30 trials) in patients resistant to vincristine and prednisone was almost identical to that in children still sensitive to vincristine and prednisone (42%, 11 of 26 trials). The complete remission rate of 38% (14 of 37 exposures) in those children who had not received L-asparaginase previously compared favorably with the complete remission rate in those children who had received prior L-asparaginase (47%, 9 of 19 exposures). Forty-seven of the 56 induction trials were in children with 1 or more remissions and 14 of these were in children with 3 or more prior remissions. Toxicity was minimal.