The effects of four heavy metal cations, cadmium 2+ (22537480), mercury 2+ (14302875), nickel 2+ (14701225), and lead 2+ (14280503), on some of the oxidative metabolic events in rat alveolar macrophages were studied. The metals used in the experiments were added to macrophage suspensions as either chloride or acetate salts. Oxygen consumption, glucose metabolism, and the release of active oxygen species were measured in macrophage suspensions at rest and during phagocytosis. All four heavy metals depressed the oxygen consumption and glucose metabolism which occurred in alveolar macrophages at rest by about 60 to 95 percent. During phagocytosis there was release of reactive forms of oxygen from the cells, a two to threefold increase in oxygen consumption, but no change in glucose metabolism from that which occurred in resting cells. Release of active oxygen from the cells and oxygen consumption during phagocytosis were inhibited 75-85% by the metals. The authors conclude that heavy metals inhibit oxidative metabolic processes in alveolar macrophages and, thus, may diminish the antibacterial activity of these cells.