It is common for general practitioners (GPs) to refer patients suspected of impaired liver function for laboratory tests (alkaline phosphatase, lactate dehydrogenase, bilirubin, prothrombin, aspartate aminotransferase). In a prospective multipractice study over a six-month period, including 30 GPs, 55 patients were recorded as having, for the first time, a high level of alkaline phosphatase (AP) as an isolated finding, 14 with an increase of aspartate aminotransferase (ASAT), eight with an increase of both AP and ASAT, three with an increase of ASAT, AP, and bilirubin, two with an isolated increase of lactate dehydrogenase (LDH), one with an increase of ASAT, AP, and bilirubin, combined with a low prothrombin (PP), and, finally, one patient with a low prothrombin in isolation. In most cases the tests were requested because of unspecific symptoms. The most common causes of abnormal test results were neoplasms, alcoholic liver disease, and heart failure. Thirty patients were referred to hospital for further investigations. During the same study period, 50 patients with known abnormal liver function tests were recorded, and the most common causes of these abnormalities were neoplasms, rheumatoid arthritis, and alcoholic liver disease.