Several lines of evidence suggest that abnormal brain serotonin metabolism may occur in early onset, type 2 alcoholism in men. Low cerebrospinal fluid 5-hydroxy-indoleacetic acid concentration has been found to be associated with a history of paternal alcoholism, and abnormal oral glucose tolerance tests (tendency to low blood glucose nadir) in subjects who are prone to exhibit impulsive, aggressive behaviour under the influence of alcohol. Moreover, a low ratio of the concentrations of tryptophan and other large neutral amino acids in plasma seems to correlate with early onset alcohol abuse and violent tendencies. More knowledge is required about neurochemical changes in homogenous subgroups of alcoholics such as the putative type 2 so as to understand which of the relationships are causative and to provide treatment strategies for alcoholism and its complications.