The biological mechanisms examined in this paper cover only a small portion of those that may be involved in the pathogenesis of alcoholism. Certain areas on which a great deal of work has already been done have been entirely omitted. Among these are studies on brain acetylcholine and gamma-aminobutyric acid metabolism in alcohol-related conditions; the effect of alcohol on brain proteins and nucleotides and the relationship of changes in these to the development of tolerance and physical dependence; and a variety of other areas involving biochemical and physiological parameters. The omission of any of these areas in no way suggests that they are less significant than those that have been covered. It is just that I have attempted to present a cohesive and coherent review of some areas of biological research which thus far appear to throw light on the clinical development and phenomenology of the alcoholism syndrome. In order to present such a thesis, I have inevitably crowded the evidence to fit some of my pet hypotheses. However, in controversial areas (which are many), I have tried to present some of the evidence on both sides and, hopefully, have succeeded in offering a fair overview of the state of the science as it exists today.