The drug discrimination paradigm was used to evaluate the contribution of dopamine or serotonin receptors in the mediation of the stimulus properties of ethanol. Briefly, rats were trained to discriminate between ethanol (600 mg/kg, IP) and water vehicle. Dose-response relationships were observed for ethanol and rats were tested with various dopamine and serotonin receptor agonists and antagonists. The specific dopamine receptor agonists SKF 38393 (DA1) and LY 171555 (DA2) failed to produce appreciable ethanol-like stimulus effects. Furthermore, the dopamine receptor antagonists SCH 23390 (DA1) and haloperidol (DA2) did not affect ethanol-appropriate responding when administered in combination with the training dose of ethanol. A number of specific serotonergic receptor ligands were also tested. Quipazine, 5-MeODMT, buspirone, 8-OH-DPAT elicited intermediate ethanol-like stimulus properties in rats. The serotonin receptor blockers pizotifen, pirenperone and (-)propranolol were ineffective in blocking the interoceptive cue produced by 600 mg/kg ethanol. However, TFMPP produced strong ethanol-like discriminative properties and completely substituted for the training dose of ethanol. These results indicate that the stimulus properties of TFMPP are similar to those of a low dose of ethanol.