Pulmonary function studies were conducted one to two days prior to, two weeks after, and an average of 116 days after coronary artery revascularization surgery. Preoperation it was found that 11 of 19 patients had mild to moderate obstruction, 8 of 17 had diffusing capacity less than 80 percent of predicted, and 9 of 17 had mild hypoxemia. Many of these abnormalities seemed related to smoking. After surgery, significant reductions in volumes, diffusion and PaO2 were found at two weeks. By the last study, there was improvement in volumes and diffusion, but they remained significantly reduced in comparison to preoperative levels. Arterial oxygen tension (PaO2) had returned to preoperative levels. Correction of diffusion for volume showed there to be no change in any of the study periods suggesting chest wall alteration is a major component of the abnormality. It is concluded that close monitoring of pulmonary function is indicated before and after operation in this patient population even if the patient is asymptomatic.