In normal volunteers and cancer patients, studies using L-(N-13)glutamate as an imaging agent showed localization of N-13 activity in the heart. Other organs that were well visualized include the liver, pancreas, and salivary glands. In ten subjects the average myocardial uptake after intravenous injection of labeled glutamate was (5.7 +/- 0.39)% (s.e.m.) of injected dose, as determined by a quantitative scanning system. The concentration of N-13 activity in the human heart could not be predicted from previous studies involving myocardial uptake in dogs and rodents after administration of L-(N-13)glutamate.