Male Jcl: Wistar rats were exposed to 2, 4, and 10 ppm NO2 for 14, 10, and 7 d, respectively, to examine the effect of NO2 on the lung glycolytic pathway, a major energy-generating system in the lung. A highly significant increase in the activities of hexokinase, phosphofructokinase, 3-phosphoglycerate kinase, pyruvate kinase (PK), and lactate dehydrogenase was observed after 5 d exposure to 10 ppm NO2, and a significantly higher value was maintained until d 7. Similarly, the activities of all enzymes examined increased significantly by exposure to 4 ppm NO2, reaching the maximum between 4 and 7 d of exposure, and then approached to near the control levels. The most remarkable increase was found in the PK activity, which reached 1.82- (p less than 0.001) and 1.53-fold (p less than 0.001) that of the control at d 5 (10 ppm) and d 7 (4 ppm) of exposure, respectively. Upon exposure to 2 ppm NO2, the PK activity of exposed animals was also increased to 1.23-fold (p less than 0.05) that of the control at d 7, and a higher activity was maintained until d 14. The glucose-6-phosphate dehydrogenase activity of exposed animals increased significantly at d 3, 4, and 14 of exposures to 10, 4, and 2 ppm NO2, respectively, and a significantly higher value was maintained in the following period of exposure. These results show that short-term exposure of rats to 2-10 ppm NO2 induces the pulmonary systems concerning glycolysis and NADPH-generation. The generation of energy and NADPH in the lung may be enhanced by NO2 inhalation.