Fourteen children with acute leukemia were treated with bi-weekly intravenous injections of methotrexate (amethopterin) after relapse during oral chemotherapy. Twelve of these children obtained a remission from the therapy with an average duration of 4.4 months for the 14 patients. The median survival time was 19.5 months for the group, with six patients still living. A statistical method based on regression analysis was used to determine the significance of the difference in the results obtained in the study group and in a control group of 36 patients treated at this hospital between 1955 and 1959. It was concluded that intravenous methotrexate therapy prolonged the survival of these patients and was a useful therapeutic adjunct.