In 66 alcoholic patients, serum gamma-glutamyl-transferase (transpeptidase) (GGTP) activity was studied in relationship to other biochemical liver function tests and histological liver damage. Elevated serum GGTP activity was the single most common biochemical abnormality (74%) and, when present was accompanied by histological abnormalities in all but one case. In seven patients, including two with alcoholic cirrhosis, this was the only biochemical abnormality. The mean serum GGTP was highest in the cirrhotic group. There was some correlation between serum GGTP activity and the degree of histological hepato-cellular necrosis. The values showed a wide scatter, however, and 12 patients had normal serum GGTP activity when histological damage was present. While elevated serum GGTP levels in alcoholism may be partly related to structural liver damage, other mechanisms, such as hepatic microsomal enzyme induction or alcoholic pancreatic damage, may also play a role.