Extragonadal germ cell tumor versus hepatocellular carcinoma must be distinguished in case of diffuse metastatic liver disease and highly elevated alpha-fetoprotein serum levels. The differential diagnosis is difficult, and conventional histological staining methods usually yield no results. However, liver puncture and immuncytology are new and reliable means for differentiation. The antibody HE A 125 reacts with all epithelial tumors including germ cell tumors, but shows no reactivity with normal or malignant hepatocytes. The practical value of this method is exemplified by the case of a 20-year-old patient with diffuse metastatic liver occupation by an extragonadal germ cell tumor.