1. Portal hypertension was produced experimentally in rats by partial constriction of the portal vein.
2. Twelve rats were injected daily with indomethacin, 4 mg/kg body weight, and 12 with the vehicle (80% ethanol, 0.5 ml/day).
3. There were no differences in portal-systemic shunts nor systemic or splanchnic haemodynamics between indomethacin-treated and untreated rats.
4. These results suggest that cyclo-oxygenase products do not play a significative role in haemodynamic alterations shown by portal-ligated rats.