SummaryInasmuch as human monocytes are able to killCandida albicans (C. albicans)only through oxidative pathways, which also produce chemiluminescence (CL), CL was used to assess the ability of polymorphonuclear neutrophils and monocytes to phagocytose and killC. albicansin a 12-year-old girl with chronic mucocutaneous candidiasis.In contrast to normal mononuclear cells (monocytes and lymphocytes), mononuclear cells from the patient did not respond with a CL burst when mixed with opsonizedC. albicans(peak CL, 55versus105 cpm x 10-3for control). Phagocytosis ofC. albicansby monocytes, assessed by electron microscopy, was normal. The patient's mononuclear cells did produce CL when mixed withCandida parapsilosis(peak CL, 68versus72 cpm x 10-3for control) or zymosan (peak CL, 149versus180 cpm x 10-3for control). Myeloperoxidase activity in monocytes assessed by light microscopy was normal. However, peroxidase activity in the patient's monocytes persisted in glass-adherent monocyte-macrophages after 5 days incubation, suggesting that her cells may mature poorly.In contrast to the poor CL response of monocytes toC. albicans, polymorphonuclear neutrophils from the patient had increased CL (peak, 858versus458 cpm x 10-3for control). Also, the patient's serum showed increased opsonic activity forC. albicans(peak, 1800versus1100 cpm x 10-3for control).