The aim of this study was to investigate the functions of monocytes obtained from 14 patients with diabetes mellitus (DM) compared with those of monocytes from healthy individuals. It was found that the total number of circulating monocytes in the 14 diabetic patients was lower than that from the healthy individuals. Phagocytosis of Candida albicans was decreased in the monocytes from the patients, whereas pinocytosis of acridine and phagocytosis of latex and sheep red blood cells were normal. The chemotactic response towards casein was enhanced. The possible consequences of these findings for the elucidation of concomitant infections in diabetic patients are discussed.