gamma-Glutamyltransferase is widely used as a marker of alcohol intake although its performance is poor. This might be related to other conditions influencing gamma-glutamyltransferase activity. The authors studied determinants of gamma-glutamyltransferase activity in a random sample (n = 6,010) drawn from the general population aged 25-64 years in Finland in 1992. In regression analysis, coffee intake and drinking boiled coffee were significantly (p < 0.01) negatively related to gamma-glutamyltransferase, whereas age, male gender, the number of cigarettes per day, serum total cholesterol and high density lipoprotein cholesterol, heart rate, and diastolic blood pressure were significantly positively related to gamma-glutamyltransferase. A significant (p = 0.02) positive interaction was observed between alcohol intake and body mass index. In logistic regression analysis, the proportion of elevated gamma-glutamyltransferase values (> or = 50 U/liter) was significantly decreased, compared with lifelong abstainers, at the alcohol intake level of < 40 g/week (odds ratio (OR) = 0.51, 95% confidence interval (CI) 0.29-0.92) and significantly increased at the level of > or = 300 g/week (OR = 2.81, 95% CI 1.35-5.85) among nonobese subjects (body mass index < 27 kg/m2). Among obese subjects, the respective proportion was significantly increased at the alcohol intake level of > or = 40 g/week (OR = 2.02, 95% CI 1.11-3.68). The proportion of elevated gamma-glutamyltransferase values was significantly decreased at the coffee intake levels of both four to six cups a day (OR = 0.44, 95% CI 0.31-0.62) and seven or more cups a day (OR = 0.36, 95% CI 0.24-0.53). In addition, drinkers of boiled coffee had elevated gamma-glutamyltransferase values more often than drinkers of filtered or instant coffee (OR = 0.59, 95% CI 0.42-0.84). No effects of alcoholic beverage preference were observed. Elevated gamma-glutamyltransferase activities appear to be related to heavy alcohol intake among the nonobese and to very light intake among obese subjects. Coffee appears to decrease gamma-glutamyltransferase activity.