ABSTRACT Three young dogs were evaluated because of the sudden development of ascites. In each case ascites was referable to non‐fibrosing hepatic disease associated with portal hypertension. Obstruction to portal flow was pre‐sinusoidal in two cases and post sinusoidal in the other. In all cases ascites developed in the absence of severe hypoalbuminaemia. The ratio of the protein content of ascitic fluid in relation to the protein content of plasma proved useful in differentiating between pre‐ and post sinusoidal portal hypertension. All three animals died or were euthanased because of the sequelae of portal hypertension.