Four patients with liver carcinoma (case 1: hepatocellular carcinoma; cases 2 and 3: metastases; case 4: adenocarcinoma possibly of hepatic origin) underwent a wedge liver biopsy taken at some distance from the tumor. Liver histology was normal in cases 2 and 3. Sinusoids were dilated in case 4. Fibrosis formed bridges between portal tracts in case 1. In all 4 cases, sinusoids contained lymphocytic cells. By electron microscopy (perfusion-fixation with glutaraldehyde) numerous lymphocytes could be identified as pit cells with characteristic dense granules and occasional rod-cored vesicles. The majority of the pit cells were luminal cells in contact with endothelial or Kupffer cells; some were in the Disse space. It is now accepted that pit cells are resident large granular lymphocytes with natural killer activity. The increase in the number of pit cells in liver carcinoma compared to the number observed in the control group (uncomplicated gallbladder lithiasis) could be hypothetically interpreted as a defense mechanism against tumor extension.