Five obese subjects were studied when they were on a 3.35 MJ (800 kcal)-diet, 1.67 MJ (400 kcal) diet and during total starvation. Urine excretion of sodium and dopamine and plasma renin activity (PRA) and plasma aldosterone levels were measured. Urine sodium excretion increased from 88 +/- 9.8 mmol/d before starvation to 150 +/- 15.7 mmol/d on day 4 of starvation. Dopamine excretion increased from 0.92 +/- 0.23 mumol/d before starvation to 1.56 +/- 0.24 mumol/d on day 1 of starvation (P less than 0.01). These results suggest that dopamine excretion is increased in early starvation and may play a role in the natriuresis of starvation.