Nine patients with liver-predominant or liver-only metastatic adenocarcinoma, who received hepatic intra-arterial and peripheral intravenous chemotherapy, were evaluated to determine if changes in plasma CEA accurately indicated changes in liver tumor volume as estimated from serial liver scan defect sizes, and if the two were quantitatively related. When selected periods of tumor remission or progression were studied during chemotherapy, the index of change of serial CEA values correlated positively (r = 0.764, P = 0.01) with the index of change of liver tumor volume in all 9 cases. Changes in absolute CEA values, however, aid not correlate significantly with changes in absolute liver tumor volumes when assessed either during these selected periods or throughout individual patient courses. Biologic and methodologic factors that influence the quantitative relation between liver tumor volume and plasma CEA are discussed.