Abnormalities in leukocyte number and function contribute to the high incidence of infection in patients with HIV infection. Leukopenia is a frequent occurrence in patients with AIDS and AIDS-related diseases and is a major dose limiting factor in the treatment of HIV infected individuals with antiviral compounds and chemotherapy. Granulocyte-macrophage colony stimulating factor (GM-CSF) is a hematopoietic hormone that stimulates the growth and differentiation of myeloid progenitor cells in vitro and enhances the function of mature monocytes and neutrophils. Studies on the effects of this agent in patients with AIDS, indicate that GM-CSF causes increased production of neutrophils, monocytes, and eosinophils in a dose dependent fashion. Leukocytes produced in response to GM-CSF function normally as judged by in vitro tests. The effects of GM-CSF on HIV replication and expression in vivo are uncertain. Studies of the use of GM-CSF alone and in combination with antiretroviral, antimicrobial, antineoplastic agents or other hematopoietins and cytokines will help define its ultimate clinical utility in patients with HIV infection.