The morphology and phagocytic capacities of pulmonary macrophages recovered by lavage from normal rats were studied in vitro after incubation under various culture conditions. Most adherent macrophages (73 +/- 6%) were flat and exhibited ruffled surfaces. Phagocytosis of carbonyl iron beads by pulmonary macrophages was quantitated using secondary and backscattered electron microscopic techniques. Our results show that macrophage surface features correlate with the phagocytic capacity of the cells, that is, macrophages with ruffled membranes phagocytose a significantly greater number of iron beads than do smooth, unruffled cells (P less than or equal to 0.001). Moreover, an enhanced percentage of smooth cells (48%) was found in populations of tracheobronchial macrophages; this finding correlated with a reduced phagocytic potential. When the percentages of smooth cells were increased experimentally by incubating cells with silica or varying pH conditions, the number of macrophages devoid of carbonyl iron beads was enhanced. The results show that smooth macrophages are functionally impaired compared with ruffled cells. These studies form the basis for assessing functional alterations of macrophages exposed in vivo to inhaled toxic particulates such as chrysotile asbestos and silica.