Polymorphonuclear neutrophils (PMNs) and their interaction with immunoglobulins constitute a major line of defence against invading Candida albicans. The function of neutrophils, assessed by superoxide production, and the opsonizing efficacy of sera from 15 AIDS patients with esophageal candidiasis and 15 healthy control subjects were studied. When stimulated with opsonized C. albicans the superoxide generation of PMNs from AIDS patients did not differ from the response observed in healthy subjects. However, a significant depression was demonstrated when PMNs were maximally stimulated by phorbol-12-myristate-13-acetate (PMA). A reduction in opsonizing capability of serum from AIDS patients was detected when tested with zymosan particles. However, the opsonizing capacities of serum from AIDS patients and control subjects were comparable in anticandidal activity, a result that may be explained by a compensatory stimulation of the specific humoral anticandidal response due to perpetual mucous candidiasis in the AIDS patients. These results suggest that anticandidal activity of PMNs and sera from AIDS patients with esophageal candidiasis is preserved, matching the clinical evidence that systemic candidiasis is seldom seen in non-neutropenic AIDS patients.