The levels of serotonin (5-HT), 5-hydroxyindoleacetic acid, tyrosine (TYR), norepinephrine (NE), acetylcholine, GABA, glutamate (GLU), aspartate (ASP), alanine, glycine (GLY) and taurine were measured in the CNS of adult male rats selectively inbred to the F8 generation for alcohol preference (P) and non-preference (NP). With respect to the values found in the NP group, higher levels of 5-HT, GABA, GLU and GLY and lower levels of ASP were found in the diencephalon-mesencephalon (D-M) and higher levels of NE were found in the telencephalon (TEL) of the P group. The animals in the P and NP strains were further subdivided into two additional groups, one given only H2O (W) and the second given 10% ethanol (A) during a one week period, thereby producing four groups (NP-W, NP-A, P-W and P-A). With these conditions, the level of (a) TYR in the D-M was higher in the P-A and NP-A animals than in the P-W and NP-W groups respectively; (b) 5-HT in the TEL was higher in the NP-A group than NP-W group; and (c) GABA in the TEL was higher in the P-A than P-W animals. No differences were observed in the cerebellum between the two strains or between the subgroups within each strain. The present study also demonstrated that the P animals will work in an operant situation to obtain 10% ethanol, even when H2O is freely available, and will voluntarily bar-press up to 6-7 times for each ethanol reinforcement.