The prevalence and significance of peripheral blood eosinophilia in patients infected with the human immunodeficiency virus (HIV) were evaluated. Fifteen of 119 consecutive patients had absolute eosinophil counts of > 450/mm3. During a mean follow-up period of 419 days eosinophilia could be identified as secondary to a parasitic infection in only one patient. Correlation with disease stage showed a higher rate of advanced disease in patients with absolute eosinophilia. In a multivariate regression analysis, only low CD4+ cell counts, not the CDC disease stage or the use of antiretroviral therapy or primary prophylaxis, contributed significantly to the prevalence of eosinophilia. It is concluded that expensive laboratory investigations in asymptomatic patients with advanced-stage HIV disease are neither necessary nor cost effective.