To assess the clinical value of positron emission tomography (PET) in the evaluation of coronary artery bypass grafting (CABG), PET perfusion and metabolic imaging using nitrogen-13 ammonia and fluorine-18 deoxyglucose (FDG) was performed before and 5 to 7 weeks after CABG in 22 patients with coronary artery disease. Postoperative improvement in hypoperfusion was observed more often in the metabolically active segments (62%) than in the inactive segments (27%) on the preoperative PET study (p less than 0.05). Similarly, the postoperative lessening of wall motion abnormality was observed more often in the metabolically active segments (78%) than in the inactive segments (22%) (p less than 0.001). Of 19 asynergic segments showing increased FDG uptake before operation, the postoperative PET revealed a decrease in FDG uptake in 13 (68%) and persistent uptake in 6 (32%). The improvement in asynergy was observed in all the segments that showed a postoperative decrease in FDG uptake, but in only 50% of those with persistent uptake (p less than 0.01). On the other hand, 4 of 5 segments showing a new FDG uptake after operation revealed further wall motion abnormality. Furthermore, the segments metabolically active before operation were more likely to have patent grafts (95%) than the metabolically inactive segments (70%) (p less than 0.05). Thus, preoperative metabolic imaging using PET appears to be useful for predicting the response to CABG. Improvement in metabolic derangement was associated with improvement in regional function after CABG.