Preoperative LDH, CPK, alkaline phosphatase and liver scan results were compared with the presence or absence of hepatic metastases at operation in 124 laparotomies in 123 patients with colorectal carcinomas during a three-year period. The overall accurcy rates for the four tests ranged from 74 to 84 per cent. The false-negative rates were acceptably low (9-13 per cent) for all but the CPK determination. The false-positive rates were unacceptably high for all four tests (38 to 60 per cent). A 'metastatic score' for reducing the high false-positive rate is described. In view of the high false-positive rates of preoperative screening tests, laparotomy is presently the most accurate method of diagnosing hepatic metastases.