1. The effect of inhibition of prostaglandin synthesis on urinary excretion of free dopamine, a catecholamine thought to act as a renal natriuretic hormone, was examined in six normal women.
2. The volunteer subjects were treated with indomethacin (2 mg day−1 kg−1) for 7 days. This regimen produced an immediate and significant but transient decrease in urinary sodium excretion, averaging about 80 mmol over a period of 3 days.
3. Urinary dopamine excretion during the control period was not different from that during the entire period of indomethacin treatment.
4. It is concluded that indomethacin does not affect urinary dopamine excretion. The change in intrarenal nervous release of dopamine in response to the sodium retention induced by indomethacin may have been too small to make a significant contribution to total urinary dopamine excretion.