Three cows with regwort (Senecio alpinus) poisoning were examined clinically, haematologically and ultrasonographically, and biopsy specimens of the liver were examined histologically. At the end of the study, the cows were euthanased and examined postmortem. The major clinical signs included severely disturbed general demeanour and behaviour, and severe diarrhoea. One cow was photosensitive. The activities of liver enzymes and the concentration of bilirubin were high in all of the cows. In two of the cows, ultrasonographic examination revealed a heavy accumulation of abdominal fluid, which was diagnosed as non-inflammatory ascites. In all the cows, the liver parenchyma was heterogeneous, and cows 1 and 2 had multiple echogenic foci 5 to 10 mm in diameter. In cow 3, the facies diaphragmatica of the liver appeared irregular in outline owing to the presence of nodules which were approximately 5 cm in diameter. The liver was also greatly enlarged and extended almost to the linea alba ventrally and beyond the reticulum cranially. All the cows had portal hypertension and the portal vein was dilated, resulting in oedema of the walls of the gall bladder, the small intestines and the omentum. The diameter of the caudal vena cava was reduced as a result of the impaired hepatic circulation. Histological examination of liver biopsy specimens revealed severe hepatic fibrosis in all the cows.