The properties of neurotransmitter receptor-effector systems were determined in C57BL/6 mice treated with 7% (v/v) ethanol and in mice selectively bred for differences in sleep time after ethanol administration. Mice treated with ethanol for 7 days and then withdrawn for 24 hours showed a decreased hypothermic response to apomorphine. There was no change in basal or dopamine-stimulated adenylate cyclase activity or in the density or affinity of the receptor for 3H-spiroperidol. A small decrease in the density of β-adrenergic receptors was observed in the cerebral cortex of alcohol-treated and withdrawn mice. This decrease was entirely due to a decrease in the density of β2-adrenergic receptors. No change was observed in cyclic AMP accumulation due to either α- or β-adrenergic receptor stimulation. Ethanol administration did result in a rapidly reversible increase in the density of muscarinic cholinergic receptors in the hippocampus and cortex.