Male Wistar rats were exposed to 4 ppm nitrogen dioxide (NO2) for 10 d, and at intervals alveolar macrophages were collected by pulmonary lavage. A metabolic enhancement of alveolar macrophages was observed on d 4 of exposure. The specific activities of glucose‐6‐phosphate dehydrogenase and glutathione peroxidase of the peroxidative metabolic pathway increased to 1.29‐fold (p< 0.001) and 1.17‐fold (p< 0.05) those of the control values, respectively. The specific activities of succinate‐cy‐tochrome c reductase of the mitochondrial respiratory system and pyruvate kinase of the glycolytic pathway also increased to 1.17‐fold (p< 0.01) and 1.20‐fold (p< 0.01) those of the control values, respectively. In addition, the incorporation of [3H]Ieucine and [14C]thymidine into alveolar macrophages were elevated to 1.77‐fold (p< 0.001) and 1.84‐fold (p< 0.01) those of the control values, respectively. The activities of all enzymes tested decreased to control levels by d 10.