DOB, 4-bromo-2,5-dimethyloxyamphetamine, a potent hallucinogen, displays high affinity for the 5-HT2 receptor in binding assays. Since 5-HT contractile responses in guinea pig trachea are mediated by 5-HT2 receptors, we assessed the activity of DOB and related analogs in this preparation. DOB acts as a partial 5-HT agonist with an EC50 = 25 nM and is blocked by the potent selective 5-HT2...