OBJECTIVES: I. Determine the maximum tolerated dose of aminopterin in patients with refractory leukemia and minimal previous exposure to antifolate agents. II. Determine the antileukemic activity of aminopterin in adults and children with acute myelogenous and acute lymphoblastic leukemia for whom conventional therapy has failed. III. Confirm that aminopterin can be administered for four consecutive weeks when followed with minimal leucovorin calcium rescue and determine the minimal amount of leucovorin calcium required for each patient. IV. Confirm bioavailability data on oral aminopterin by performing limited sampling pharmacokinetics. V. Correlate blast uptake of aminopterin in vitro with clinical response.