The effects of nickel chloride inhalation on the enhancement of experimentally induced streptococcal infections were studied. Exposure to nickel chloride for 2 hr produced significant enhancement in mortality. This response was observed for 24 hr after the nickel chloride exposure. A delayed clearance response of inhaled streptococci, also observed in the nickel-treated mice, supported the mortality data. Several parameters involving pulmonary cells obtained by in situ lavage 24 hr after nickel chloride exposure were also studied; no reduction in total cell yield, viability, or cellular composition was observed. A significant reduction in phagocytic capability, as compared to that of control animal cells, was observed in alveolar macrophages obtained 24 hr after nickel chloride exposure.