Isotopic scanning of the liver to detect hepatic metastases is a commonly used clinical tool in assessing the extent of malignant disease and the proper mode of therapy. Opinions vary widely as to the efficacy of this test. To determine the accuracy of our scanning technique the clinical and laboratory data on 429 patients who had hepatic scans (technetium sulfur colloid) between February 1971 and May 1973 was reviewed. Of these patients, 125 had a confirmatory procedure (needle biopsy - 15, abdominal exploration - 69, autopsy - 41) done within 6 weeks of their scan. Nineteen patients who had negative scans were proven to have hepatic metastases. Fourteen patients had positive scans which could not be substantiated by one or more of the above confirming examinations. Thus the frequency of error was 25%. Regarding other tests - alkaline phosphatase and bilirubin - no better correlation could be made with respect to the presence or absence of metastases. From the data available on this small group of patients the liver scan is sufficiently inaccurate to preclude relying upon it for the selection of therapy in cancer patients. When the presence of hepatic metastases changes the type of therapy a confirmatory laparotomy or biopsy should be considered.