In six healthy volunteers plasma concentrations of adrenaline, noradrenaline and dopamine were measured at rest and during dynamic forearm exercise at submaximal and maximal intensities. Arterial and venous concentrations of adrenaline and noradrenaline increased with forearm exercise at all workloads. Dopamine concentrations did not change. The increases in adrenaline and noradrenaline were almost linearly related to the increase in heart rate with no levelling off at maximal exercise intensities. It is concluded that dynamic exercise with the forearm muscle group causes a small but significant activation of the sympatho-adrenal system as reflected by increases in plasma concentrations of adrenaline and noradrenaline.