Polymorphonuclear cell (PMN) chemotaxis, phagocytosis, killing, superoxide anion (O2-) generation and enzyme release were evaluated in 20 malnourished aged individuals. PMN from malnourished elderly exhibited a significant reduction of their functional capacities, while no differences in terms of enzyme release by the same cell suspensions were observed in comparison to young well-nourished donors. By contrast, a diminished total cell myeloperoxidase amount and high level of O2- generation were detected. In vitro vitamin and/or trace element pretreatment of cells from aged subjects gave rise to a significant enhancement of their chemotactic, phagocytic and killing capacities. In addition, such an experimental approach led to an augmented total cell myeloperoxidase level and to an O2- generation which fell within normal values. Taken together, these findings suggest that malnutrition may represent an additional factor involved in the decline of PMN responsiveness in the elderly.