The whole body clearance of noradrenaline (NA) was measured in seven patients pre- and postoperatively. L-3H-NA was infused intravenously for 90 min and steady-state concentrations of L-3H-NA were measured in both arterial and peripheral venous blood. Preoperatively, in the resting supine position the clearance values based on arterial and venous sampling averaged 1.4 and 2.5 l/min, respectively (p less than 0.02). The difference in clearance values was due to peripheral uptake of NA averaging 45%. The plasma appearance rate on NA averaged 2.4 nmol/min before surgery and it increased to 9.5 nmol/min postoperatively (p less than 0.02). The plasma clearance of NA did not change. These results indicate that the calculation of plasma NA clearance based on venous sampling results in values that are too high. Furthermore, such values may be influenced by individual variations in the peripheral uptake of NA, since we found no correlation between clearance values based on venous and arterial sampling. In other experiments we measured the influence of physical exercise in young healthy subjects on the clearance rate of plasma adrenaline (A). The clearance of A, which at rest averaged 1.9 l/min tended to increase at low work loads and to decrease below resting levels at high exercise intensity. The changes were, however, small (+/- 20% of resting values). The regional extraction ratio of NA was 0.5 to 0.6 in the forearm, the liver and the kidney.(ABSTRACT TRUNCATED AT 250 WORDS)