Fractional myocardial extraction/release of glutamate, glutamine, alanine, ammonia, asparagine, glucose and lactate was studied in 12 subjects with normal coronary anatomy (controls) and 28 patients with coronary artery disease (CAD) during rest and atrial pacing. At rest patients with CAD showed an increased myocardial extraction of glutamate, glucose and lactate and an augmented glutamine and alanine release compared with controls. In all CAD patients myocardial ammonia and asparagine release was found at rest, while all controls showed myocardial extraction of these compounds. Myocardial glutamate extraction correlated positively with glucose and lactate extraction, glutamine and alanine release and inversely with ammonia release in CAD patients at rest. In patients with two- and three-vessel disease pacing-induced ischaemia resulted in a pronounced decrease in myocardial glutamate extraction and glutamine release, augmented myocardial production of ammonia and asparagine and a conversion of lactate extraction into lactate release. During pacing myocardial glutamate extraction was related to alanine and glutamine release and correlated inversely with ammonia and lactate release in these patients. The results indicate that glutamate extraction is closely connected with glucose and lactate extraction and ammonia binding via glutamine formation in the hearts of CAD patients and, thus, with the energy supply of ischaemic myocardium. An assessment of myocardial exchange of the nitrogenous compounds we have studied, complimentary to lactate, is a promising biochemical test for the identification of ischaemic heart disease in man.