A technique for quantifying nonspecific phagocytosis of alveolar and peritoneal macrophages in the same animal has been developed utilizing fluorescent polystyrene beads. When incorporated into inhalation studies, the technique can be used to determine whether the toxic effect of an inhaled pollutant is local (effect on alveolar macrophages), systemic (effect on peritoneal macrophages), or both local and systemic. The method results in a determination of the percent phagocytic macrophages and of the degree of individual macrophage phagocytic activity based on the number of beads phagocytized per macrophage. Macrophage preparations were incubated with fluorescent beads for 2 hr and cytocentrifuged onto a glass slide. Fluorescent beads present on the slide or cell-associated but not ingested by phagocytosis were removed by immersing the slide containing the macrophago preparation in methylene chloride for 30-60 sec. Fluorescent beads ingested by phagocytosis were then easily quantified with a fluorescence microscope. (Copyright (c) 1987 by the Society for Experimental Biology and Medicine.)