Histological changes of the pulmonary vasculature in comparison with that of the portal vein in necropsy cases of severe hepatic injury that had not been associated with clinical pulmonary hypertension were analysed qualitatively and quantitatively. The main changes of the intra-hepatic portal vein were dilatation (88.3 per cent), thickening of the wall (58.5 per cent) and thrombi (22.3 per cent). The changes of the pulmonary vasculature were limited to muscular type arteries, which showed dilatation (31.9 per cent), thickening of the wall (30.9 per cent) and thrombi (10.6 per cent). Association of wall thickening of the portal vein and the small pulmonary artery was observed in 30.9 per cent, these associations being statistically significant. Coincidence of thrombus formation in the portal vein and pulmonary vasculature was observed only in 4.3 per cent, which was not statistically significant. After the circumferences of the internal and external elastic laminae of small pulmonary arteries and the cross-sectional area of the media were measured, the anatomical radius and wall thickness of each artery were calculated according to Furuyama 's method. The relations between the anatomical radii and wall thickness of small pulmonary arteries in controls and hepatic cirrhosis groups were investigated by analysis of covariance to compare the equality of the two corresponding regression lines. The wall thickness and the ratio of wall thickness to the anatomical radius of small pulmonary arteries were significantly larger in the cirrhotic group than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)