Proximal and distal segments of the tail artery were taken from normotensive Sprague-Dawley rats. Field stimulation (0.3-30 Hz) of periarterial sympathetic nerves elicited vasoconstrictor responses which were antagonized by prazosin (0.1-10 nM) to a much lesser extent in distal than in proximal segments. The selective alpha 2-adrenoceptor antagonist idazoxan (100 nM) alone had little effect in either segment; however in combination with prazosin vasoconstrictor responses were markedly reduced in distal segments. It is concluded that postjunctional alpha 2-adrenoceptors substantially mediate sympathetic vasoconstriction in distal segments of Sprague-Dawley rat tail artery and that this in vitro preparation may be a useful model for elucidating and extending data obtained in vivo in the human forearm circulation (Van Brummelen et al., 1983).