Medetomidine is a potent, highly selective α2-adrenoceptor agonist (Ki values are 1.08 and 1750 nM for α2- and α1-adrenoceptors respectively). Medetomidine displays greater selectivity over α1-adrenoceptors than clonidine and UK 14,304 (1620-, 220- and 300-fold respectively). Medetomidine inhibits twitch response in electrically stimulated mouse vas deferens (pD2 = 9.0). Active in vivo; displays hypotensive, bradycardic, sedative, anxiolytic, hypothermic and analgesic effects.