The influence of increasing glucose concentrations on some essential functions in polymorphonuclear neutrophils (PMN) was evaluatedin vitro in 20 healthy persons. PMN chemotaxis, adherence, phagocytosis and bactericidal capacity were estimated. Higher than physiologic glucose concentrations were found to diminish chemotaxis, phagocytosis and bactericidal capacity. The results obtained may indicate another possible mechanism that accounts for the increased susceptibility to infection observed in diabetic patients. However, PMN adherence rose parallel with increasing glucose concentrations reaching maximum values at 300 mg/dl (16.6 mmol/l). The changes of PMN adherence may suggest the participation of these cells in the development of microangiopathic injuries.