The influence of the level of serum y-glutamyl transpeptidase, a biological marker of alcohol consumption, on elevations of blood pressure and on the development of hypertension related to increases in alcohol consumption was determined in a cross-sectional study of 1,492 middle-aged male workers and in a subsequent 5-year follow-up study of 1,393 workers. Blood pressure levels, as well as the prevalence and incidence of hypertension, were higher in the subjects with serum y-glutamyl transpeptidase levels above 50 units/1 than in those with normal levels. These differences were more marked in drinkers who consumed 30 ml or more of alcohol per day. Thus, elevated serum y-glutamyl transpeptidase activity may identify drinkers at higher risk for the development of alcohol-related hypertension. {Hypertension 1991;18:819-826)