Ethanol is known to be anxiolytic and this effect may be mediated through GABA transmission acting on the GABAA-benzodiazepine-Cl- ionophore complex. Recent studies from our laboratory have suggested that GABA transmission and the GABAA-benzodiazepine-Cl- ionophore complex might be involved in the rewarding action of ethanol in alcohol-preferring rats. We report here immunocytochemical and morphometric studies analyzing the GABAergic terminal density in the nucleus accumbens (NA), corpus striatum, nucleus tractus solitarius, and lateral septum of the selectively bred P (alcohol-preferring) and the NP (alcohol-nonpreferring) lines of rats, as well as of the high-alcohol-drinking (HAD) and low-alcohol-drinking (LAD) lines of rats. The NA was included for analysis because this structure has been implicated as an important component of the brain reward system. An increase of GABAergic terminal density was found in the NA of the P rats, when compared with the NP rats. Similarly, there were more GABAergic terminals in the NA of HAD rats than of the LAD rats. No differences between the lines were seen in the other brain regions examined. The results suggest that alcohol preference in P and HAD rats may be related to increased GABA terminals and enhanced GABAergic inhibition within the NA.