Plasma CEA values and serum γ glutamyl transpeptidase activities have been compared in control subjects and 109 patients with colorectal carcinoma and 35 with non-malignant hepatic disease. CEA values alone differentiate hepatic metastases from non-malignant hepatic disease with a high degree of certainty. While CEA may be elevated with metastases, irrespective of site, γGT is elevated mainly in association with hepatic metastases. The combination of CEA and γGT is helpful in identifying hepatic metastases and in their differentiation from local recurrences or metastases to other sites.