12 subjects have been studied after an overnight fast with trace amounts of pyruvate-3-(14)C and glucose-6-(14)C. Blood disappearance curves and incorporation of the pyruvate-3-(14)C label into blood glucose have been determined. By the use of transfer functions which allow processes with many different chemical steps to be examined as a unit, we have determined the per cent of pyruvate and presumably lactate which is regenerated into glucose. 8 of the 12 subjects showed that 7-23 mg/kg per hr are recycled, while 4 subjects fell well outside this range. Correlation of increased activity was not good with any demonstrated metabolic abnormality (diabetes or obesity), and it is suggested from clinical observation of the subjects that anxiety may play a role.