A sensitive and economic method of screening for liver metastases in patients with colorectal cancer was developed using serum alkaline phosphatase and carcinoembryonic antigen. The upper limit of normal for alkaline phosphatase and carcinoembryonic antigen did not represent the optimal levels for use in predicting liver metastases. However, with alkaline phosphatase greater than 135 I.U., and/or carcinoembryonic antigen greater than 10 ng/ml, sensitivity was 88%: 23 of 26 patients with liver metastases fulfilled either or both criteria. The false-positive rate was 12%. Liver scanning, alone, demonstrated metastases in only 69% of 35 patients with liver metastases. The combination of alkaline phosphatase and carcinoembryonic antigen can be used economically to screen for liver metastases, and to determine which patients should undergo a liver scan.