When a human kidney is transplanted, sympathetic nerves to that kidney are cut. We infused3H-noradrenaline and then measured noradrenaline, dopamine and3H-noradrenaline levels in the plasma and urine of renal transplant recipients and uninephrectomized control subjects. Less than 10% of3H-noradrenaline cleared from the plasma appeared in the urine. Noradrenaline and dopamine appeared in the urine of transplant recipients at one-third the rate of control subjects, even though3H-noradrenaline levels were slightly higher in the urine of transplant recipients. Transplant patients had a noradrenaline clearance of 128 ± 50ml/min, compatible with simple glomerular filtration, while controls had a higher calculated clearance of 229 ± 41 ml/min. Plasma dopamine levels were very low compared with urinary dopamine. These results suggest that two-thirds of renal noradrenaline and dopamine depend on the presence of renal nerves. Almost all urinary dopamine comes from the kidney. For noradrenaline, urinary excretion is a very minor pathway for clearance from the plasma.