Seven neutropenic patients with the acquired immunodeficiency syndrome (AIDS) or AIDS-related complex (ARC) were treated with recombinant human GM-CSF in an attempt to reverse their leukopenia. Overall, treatment was associated with a rapid, substantial increase in neutrophilic granulocytes and a smaller increment in eosinophils and monocytes. No significant increase in platelets or reticulocytes was observed. Termination of treatment was associated with a rapid drop in the leukocyte count. While some patients with severely hypoplastic marrows did not respond to GM-CSF treatment, azidothymidine- or ganciclovir-induced neutropenia was reversed by concomitant administration of GM-CSF in others. This indicates that rhGM-CSF may be a valuable adjunct to antiviral therapy in ARC/ AIDS and requires further testing in controlled trials.