The study of the phagocytosis and intracellular killing of Candida albicans by granulocytes and monocytes has been hampered by the budding and pseudomycelium formation of this yeast during a relatively short incubation period at 37 degrees C and by the similar density of candida cells and phagocytes, which makes differential centrifugation impossible. In the present study, C. albicans was used after 5 days of preculture at 30 degrees C, after which the number of candida cells remained constant during incubation at 37 degrees C for 90 min. On this basis, phagocytosis and intracellular killing were limited to a period of 60 min. Phagocytosis of C. albicans by granulocytes and monocytes was measured with a hemocytometer, the number of extracellular candida being a measure of the ingestion of these microorganisms. After 60 min, 96% of the candida cells were ingested by normal human granulocytes and monocytes. This process was dependent on the opsonin concentration and temperature and was inhibited by mono-iodoacetic acid. Heat-inactivated serum was less active than fresh serum, reflecting the role of complement factors with respect to opsonization. Intracellular killing was measured by a microbiological assay. After 60 min of incubation of phagocytes together with C. albicans and serum, human granulocytes and monocytes killed 58 and 50% of the ingested candida, respectively. This process was inhibited by phenylbutazone. Phagocytes from patients with chronic granulomatous disease showed impaired intracellular killing.