Hepatic venography was performed on 80 patients with hepatic tumours for the pre-operative assessment of resectability. Sixty-six patients subsequently underwent laparotomy, 27 undergoing hepatic resection. Forty-two patients had metastases from colo-rectal primaries, 19 hepatocellular carcinoma and 19 a variety of other tumours. The type and frequency of the abnormalities shown on venography were noted for each tumour category and for their hepatic segmental distribution. The results of venography were compared with those of arteriography, computed tomography and ultrasound and with the findings at laparotomy. Displacement was the commonest abnormality seen while encasement or obstruction occurred less frequently and tumour invasion was rare. The sensitivity of venography in correctly identifying the segmental distribution of tumour deposits was 41%. Sensitivity was poorest with tumours in the left lobe (31%) and bilobar tumours (0%). Venography was most sensitive in detecting tumour involvement of the major segmental hepatic veins and inferior vena cava (100%). Peripheral colo-rectal metastases frequently produced no venographic abnormality. Hepatic venography provides no additional information to arteriography, computed tomography or ultrasound in patients with peripheral or bilobar tumour deposits. Some additional information may be obtained with central tumours and venography is the most accurate means of detecting tumour involvement of the major segmental hepatic veins.