Twenty-seven patients receiving a standard cytosine arabinoside and daunorubicin regimen as induction of reinduction therapy of acute myelogenous leukemia were randomly assigned to receive lithium carbonate, 300 mg t.i.d., or no lithium. Treatment groups were comparable with respect to age and baseline granulocyte counts. All patients developed granulocyte nadirs below 100/cu mm. By actuarial analysis, the median duration of granulocytopenia, less than 1000/cu mm, was 16.0 days in the lithium group and 24.6 days in the no-lithium group, p = 0.013. The median duration of granulocytes less than 500/cu mm also favored the lithium group but only approached statistical significance: 14.0 days versus 20.5 days, p = 0.054. Lithium levels between 0.5 and 1.0 meq/liter were easily maintained in 11 of 12 patients receiving lithium, 300 mg t.i.d., and toxicity directly attributable to lithium was not observed. Despite the shortened duration of neutropenia, the incidence of infections and the rate of remission were not affected.