In order to investigate the reason for the elevation of serum gamma-glutamyltranspeptidase (GGT) after chronic alcohol consumption, the activity of this enzyme, together with the activities of aspartate aminotransferase, alanine aminotransferase and alkaline phosphatase in serum (parameters of liver cell damage) and the excretion of D-glucaric acid (D-GA) in urine (parameter of microsomal enzymatic induction) were determined in 72 chronic alcoholics. Of these, 32 had no significant liver disease (1st group) and 40 had an overt liver disease varying from fatty liver to liver cirrhosis (2nd group). The GGT was elevated in only 62% of the patients of the first group, but in 95% of the second group. Of the latter group, patients with cirrhosis had significantly higher GGT mean levels than the patients with fatty liver. On the other hand, increased D-GA excretion was only found in 23% of the group 1 patients and in 44% of the group 2 patients. Moreover, in all patients there was a significant correlation between the values of GGT and aspartate aminotransferase, but not between GGT and D-GA. From these results, the GGT increase in chronic alcoholics, would seem to be better related to cellular damage than to enzymatic induction assessed on the basis of D-GA urinary excretion.