The migration inhibiting factor (MIF) test was performed on 27 patients with chronic neutropenia using acute myeloblastic leukemia (AML) blasts and normal lymphocytes as antigens. Eight patients reacted positively to AML blasts, and the natural history of their disease differed from that of the remaining neutropenic patients: two of the eight patients developed AML and one showed evidence of preleukemic changes. Recurrent severe infections were common and one patient in this group developed systemic lupus erythematosus. The MIF test toward AML blasts may be regarded as a warning sign of a preleukemic state among neutropenic patients.