1. Myocardial exchanges of plasma alanine, glutamate, citrate, lactate, glucose and free fatty acids were determined in 17 patients with coronary artery disease and in seven control subjects during rest, atrial pacing and recovery. 2. Myocardial release of alanine was demonstrated in all subjects. The amount released was higher in patients with coronary artery disease than in controls. In the patients alanine release was related to severity of coronary artery stenosis. 3. All subjects showed myocardial uptake of glutamate, higher in patients than in controls at rest and during recovery. During atrial pacing myocardial glutamate extraction remained unchanged in controls but decreased in patients. 4. Citrate was released by the heart in all controls and patients. During recovery citrate output was higher in patients than in controls. 5. Myocardial alanine and citrate release during recovery were positively correlated. Both were positively related to myocardial uptake of glutamate during recovery and to the decrease in glutamate extraction during pacing. 6. The results indicate changed myocardial citrate and amino acid metabolism in coronary artery disease. Measurement of myocardial exchanges of glutamate, alanine and citrate in addition to lactate is suggested as a sensitive biochemical test in assessing myocardial ischaemia in man.