The effects of repeated exposure to ozone on the levels and solubility of collagen in mouse and rat lungs and in rat skin were studied. The lung collagen levels of mice exposed to 0.2 to 1.7ppm ozone for 5 days remained unchanged, although GSH levels indicate the effects of ozone increased as a function of ozone concentration. A significant increase in lung collagen occurred in mice exposed to 1.0ppm ozone for 40 days. Raised collagen levels decreased more slowly than GSH levels after animals were returned to the original pre-experimental conditions. Collagen in mouse and rat lungs was almost completely insoluble in 0.5M sodium chloride, 0.5M acetic acid, or 0.2M cysteamine solutions. This insolubility continued when rats were exposed to 1.0ppm ozone for up to 10 weeks. Amounts and solubility of collagen in rat skin were also unchanged following exposure to 1.0ppm ozone for 10 weeks.