Levamisole is a synthetic, orally administered, relatively nontoxic compound with immunorestorative ability. Levamisole was tested in this study of 60 adults with acute nonlymphocytic leukemia (ANLL) to determine if augmentation of response rate or duration, or survival over that obtained with a standard chemotherapy regimen alone would result. The chemotherapy regimens for all patients consisted of daunorubicin and cytosine arabinoside for induction and consolidation, methotrexate with citrovorum factor reversal in a cytoreductive phase, and late intensification with thioguanine and cytosine arabinoside. The first 30 patients received chemotherapy alone; a second group of 30 patients were scheduled to receive levamisole in addition to chemotherapy. Levamisole, 45 mg/m2, was administered orally twice daily for three consecutive days each week beginning one week after the initiation of induction chemotherapy and continuing until relapse. No significant difference emerged between the two groups with respect to remission rate, time to achieve remission, postrelapse survival, or total survival. However, a trend towards improved postcomplete remission survival (P = 0.072) was noted in the levamisole group, and patients who received levamisole had a significantly greater reinduction rate after relapse (P = 0.019).