A study was made of the metabolism by a human subject of adenine administered intravenously at a dose of 10 mg/kg with 200 micronCi of 8-14C-adenine to learn how similar and different the results might be from those obtained by a much more extensive study by this Laboratory on the rabbit. A rapid initial disappearance of radioactivity from the blood was followed by a slower loss with a half-life of about an hour. The first was probably due to diffusion into the extravascular fluid and the second to metabolism in the tissues. Fifteen per cent of the radioactivity infused was excreted in the urine during the first three hours as unchanged adenine and another 8 per cent was excreted during the first six hours as a mixture, in almost equal parts, of 8-oxyadenine and 2,8-dioxyadenine. Radioactivity in the urine after the second day, starting at 1.5 per cent of the dose per day and declining steadily to 0.5 per cent at three months, was predominantly in uric acid, reflecting turnover of the adenine which had entered body pools of purine nucleotide. Approximately 2 per cent of the injected radioactivity was incorporated into red blood cell AMP, ADP and ATP, each of which, by the second day, had the same specific radioactivity, which then decayed at a rate of 1.3 per cent per day. The results were remarkably similar to those obtained in a previous study on the rabbit. A variety of clinical observations and tests on blood and urine showed no abnormalities attributable to the infusion with adenine.