We present a study of 107 in-patients of a detoxification center. As expected, 81 percent of them showed upon admittance an increased serum gamma glutamyl transferase (GGT). After alcohol withdrawal, GGT decreased in all but one of these patients. More surprisingly, even among the rest of the patients exhibiting upon admittance a GGT result within the reference range, there still occurred a significant decrease in 50 percent of the cases. Thus, whether the initial GGT is high or normal, we observed a decrease in 96 patients out of 107, i.e., a sensitivity of 0.90. The decrease test consists in asking a subject to refrain from any alcohol intake during a short period, e.g., seven days. If any significant diminution of serum GGT occurs, the possibility of alcohol abuse should at least be given serious consideration before being rejected. This test was used up to now only when GGT was initially high. The present results show that it can be attempted even when GGT is initially within the normal range, with a sensitivity of 0.90.