Three exposure regimens were used to study the effects of inhaled phosgene (COC12). Rats were sacrificed (1) immediately or throughout a 38 day recovery period after inhalation of 1 ppm COC12 for 4 hrs, (2) at intervals during a 7 hr exposure to 1 ppm phosgene, or (3) at several time points throughout a 17 day exposure to 0.125 and 0.25 ppm COC12 (4 hr/day, 5 days/wk) and during a 21 day recovery period. Regimen 1 revealed significantly elevated lung wet weight, lung nonprotein sulfhydryl (NPSH) content, and glucose-6-phosphate dehydrogenase (G6PD) activity which stayed elevated for up to 14 days. A significant decrease in body weight and food intake was observed 1 day after exposure. Regimen 2 caused a slight depression in NPSH content but did not affect G6PD. Regimen 3 animals showed sustained elevations in lung weight, NPSH content, and G6PD activity after 7 days of exposure. No significant changes in these endpoints were observed for the 0.125 ppm COC12 group. No consistent elevation in hydroxyproline content was seen at either exposure concentration. Light microscopic examination of lung tissues exposed to 0.25 ppm COC12 for 17 days revealed moderate multifocal accumulation of mononuclear cells in the centriacinar region. In summary, exposure to COC12 caused changes similar in most ways to those observed for other lower respiratory tract irritants. (Copyright (c) 1986 by Hemisphere Publishing Corporation.)