The effects of acute or chronic ethanol treatment and of withdrawal (24 h) after chronic ethanol treatment on 5HT 1 B receptor subtypes in different regions of the rat brain were investigated. Male Sprague-Dawley rats were fed the ethanol (9% v/v)-containing Lieber-DeCarli liquid diet or the control liquid diet for 1 day in the acute study and for 15 days in the chronic study. The ethanol-withdrawn group received the Lieber-DeCarli control liquid diet instead of the ethanol diet on the 15th night. Ethanol-withdrawn rats after 15 days of ethanol treatment were rated for withdrawal symptoms (e.g. hyperactivity, piloerection, squealing, and enhanced startle reflex) and were found to exhibit such symptoms after 24 h of ethanol withdrawal. The rats were decapitated, and cortices, cerebelli, striata, and hippocampi were separated for measurement of 5HT 1 B receptors by receptor binding techniques using 1 2 5 I-cyanopindolol (CYP) as the ligand. It was observed that acute ethanol treatment had no significant effect on the maximum number of binding sites (B m a x ) or the apparent dissociation constant (K D ) of 5HT 1 B receptor binding sites in the various brain regions. On the other hand, chronic ethanol treatment produced a significant increase in B m a x of 1 2 5 I-CYP binding to 5HT 1 B receptors in the rat cortex and hippocampus, which remained increased after 24 h of ethanol withdrawal. In contrast, in the striatum and the cerebellum of chronic ethanol-treated and withdrawn rats, the 5HT 1 B binding parameters (B m a x and K D ) were unchanged. These results suggest the possible involvement of cortical and hippocampal 5HT 1 B receptors in ethanol dependence.