Patients infected with human immunodeficiency virus (HIV) frequently are said to have eosinophilia. To evaluate this assumption, the differential blood cell counts of 855 HIV-infected patients were examined over 4 years. All differential cell lines in the HIV-infected population were less than those in a noninfected control group, but the difference was much less pronounced for eosinophils than for the other blood cell components. For HIV-infected patients, the eosinophil count increased and the other blood cell components decreased as the CD4 cell count decreased. The increase in eosinophils was the result of eosinophilia in a subgroup of patients and a preservation of that cell line for the other patients. No etiologic agent was associated with eosinophilia; hence, HIV infection itself may induce proliferation of eosinophils while other cell components are declining.