The authors examined the relationship between animal age and pulmonary biochemical effects of O3 exposure using young to adult rats ranging in age from 24 to 90 days. Glucose uptake and production of pyruvate and lactate, determined in lung tissue slices, were used as indices of O3-produced metabolic alterations. In control rats, the lung weights increased with animal age until they stabilized between 60 and 90 days of age. The rate of glucose metabolism, expressed per lung, increased with animal age paralleling the increase in lung weights. After exposure to 0.8 ppm (1568 ug/m3)O3 for 3 days, the lung weights and all three parameters of glucose metabolism increased in exposed rats relative to their age-matched controls.