The effect of aerosols of cadmium chloride (CdCl2) and cadmium oxide (CdO) on pulmonary biochemical function were compared. Rats and rabbits were exposed to 0.25, 0.45 or 4.5 mg Cd/cu. m. for 2 hr. Pulmonary toxicity was determined histologically and biochemically. Cadmium chloride and CdO showed a deposition response that was linearly related to the chamber concentration. Both compounds caused multifocal, interstitial pneumonitis 72 hr after exposure, but the CdO lesion was more severe with proliferation of fibrocytic-like cells as well as pneumocytes. Comparing the two Cd compounds at the highest concentration 4.5 mg Cd/cu. m., the biochemical responses in the rat were similar. The majority of the effects occurred 72 hr after exposure with significant increases in: lung weight, lung to body weight ratio, homogenate and supernatant total protein, GSH-reductase, GSH-transferase, and G-6-PDH. However, GSH-peroxidase was inhibited immediately after the CdO exposure.