Selective breeding of rats for differing impairment of spontaneous motor activity after 1.5 g ethyl alcohol per kg is now in the 16th generation. The MA strain shows a large decrement (80 plus percent) of activity in the 16 to 30 minute period after alcohol injection while the decrement in the LA strain is so much less as to have no overlap in this measure between the strains. Because these strains show no differences in the absorption of alcohol or in the rate of its disappearance, the strain difference is considered to be functional and at a central level. A wide variety of developmental, behavioral and biochemical measures have not as yet provided a clue as to the biochemical or neurobiological basis of the strain difference, although the difference, as in certain mouse strains (SS and LS), may well be more or less restricted to alcohols, rather than extending, for example to barbiturates. Because alcohol may have quite different pharmacodynamic utility in these strains, one of these strains may provide a suitable strain, under appropriate environmental manipulation, for an animal model of alcoholism. BIBLIOGRAPHIC REFERENCES: Worsham, E.D., Riley, E.P., Anandam, N., Lister, P., Freed, E. X. and Lester, D. Selective breeding of rats for differences in reactivity to alcohol. An approach to an animal model of alcoholism. III. Some physical and behavioral measures. In: Alcohol Intoxication and Withdrawal, III. Advances in Experimental Medicine and Biology. Ed.: Gross, M.M. Plenum Press, New York, 1977. in press. Lester, D., Lin, G. W-J., Anandam, N., Riley, E.P., Worsham, E. D. and Freed, E. X. Selective breeding of rats for differences in reactivity to alcohol. An approach to an animal model of alcoholism. IV. Some behavioral and chemical measures. In: Vol. III. Alcohol and Aldehyde Metabolizing Systems. Eds.: Thurman, R.G., Williamson, J. G., Drott, H. and Chance, B. Academic Press, New York, 1977. In press.