Flow cytometry was used to study phagocytic function and release of reactive oxygen products following phagocytosis by neutrophils (PMNL) and monocytes of heparinized whole blood from stage 1 human immunodeficiency virus type 1 (HIV-1)-infected men. Phagocytic capacity was assessed by measuring uptake of Texas red-labeled bacteria. Reactive oxygen generation after phagocytosis was estimated by the quantity of dichlorofluorescein diacetate converted to dichlorofluorescein intracellularly. Compared with results in samples from age- and sex-matched controls, PMNL and monocytes from HIV-1-infected patients exhibited a significantly increased capacity to phagocytose Staphylococcus aureus and Escherichia coli and generate reactive oxygen products. These results are consistent with the hypothesis that stimuli associated with early HIV-1 infection enhance the nonspecific response of phagocytic cells to potential bacterial pathogens.