Adrenaline infusion of 0.1 microgram.kg-1.min-1 in healthy volunteers results in an increase of hepatic glucose production, an increase of the absolute number of occupied beta-adrenoceptors and specific changes in metabolism. To compare these effects with the changes induced by an endogenous catecholamine release, we investigated healthy volunteers during cycle ergometry. After fasting at least 14 h seven healthy subjects exercised for 90 min at an intensity of 20% below their individual anaerobic threshold. The rate of glucose production as well as the turnover rates of alanine and leucine were calculated using stable isotope tracers. High and low affinity beta-adrenergic binding sites on lymphocytes were determined by an equilibrium binding assay with (-)125 Iodocyanopindolol. After 90 min of cycling the rate of appearance of glucose increased significantly from means of 2.0 (SD 0.2) to 2.65 (SD 0.50) mg.kg-1.min-1 with unchanged blood concentrations of glucose and lactate. The flux of the amino acids alanine and leucine decreased significantly from means of 0.91 (SD 0.21) to 0.62 (SD 0.14) mg.kg-1.min-1 and from 0.40 (SD 0.05) to 0.32 (SD 0.04) mg.kg-1.min-1, respectively. The mean free fatty acid concentration increased significantly from 0.65 (SD 0.33) to 1.27 (SD 0.45) mmol.l-1 during the endurance trial. The increase of glucose turnover and the decrease of amino acid flux point to a metabolic shift towards enhanced utilization of free fatty acids. Adrenaline and noradrenaline concentrations showed a moderate but significant increase from means of 0.61 (SD 0.20) to 0.99 (SD 0.36) nmol.l-1 and from 2.27 (SD 0.75) to 3.46 (SD 0.38) nmol.l-1, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)