It is known that coronary artery bypass grafting (CABG) results in impairment of postoperative pulmonary function. There is also a high incidence of pleural changes (pleural effusion or pleural thickening) after CABG. We hypothesized that those patients with pleural changes in the postoperative period would have a greater decrease in pulmonary function test (PFTs) results. The present study reports the results of 110 male patients who underwent CABG. The chest films and the PFT results obtained preoperatively and on the sixth postoperative day were reviewed. The relationship between pleural changes and PFTs was analyzed in patients who received saphenous vein graft alone (SVG group: 50 patients) or in combination with internal mammary artery grafting (IMA group: 60 patients). In the IMA group, the patients who had pleural changes had significantly greater decreases in their pulmonary function than did the patients without pleural changes. The decrease in the FVC, TLC and FEV1 in the patients with pleural effusions (37.6, 27.8 and 36.8 percent) was similar to that in patients with pleural thickening (34.6, 28.3 and 35.0 percent) and both were significantly greater (p < 0.05) than the changes in the patients with a normal radiograph (26.1, 17.6 and 26.9 percent). In the SVG group, the presence of pleural changes was not significantly related to the decrement in pulmonary function. The values of RV, FRC, Cst, and blood gases were not affected in the SVG or IMA group by the presence of pleural changes. We conclude that the presence of pleural changes on the chest radiograph is associated with a larger decrement of pulmonary function after CABG in the IMA group. This larger decrease probably reflects added thoracic trauma and is not due to the presence of pleural changes per se.