In order to investigate the characteristics of vascular alpha(2)-adrenoceptor (alpha(2)-AR) and its relation to alpha(1)-AR, isolated Wistar rat (10 weeks) aortae were used as a model for testing contractile function in vivo. It was found that both alpha(1) and alpha(2)-AR (mainly alpha(1)-AR) mediated the contractile response. While alpha(1)-AR enhanced the contractile response mediated by alpha(2)-AR, alpha(2)-AR had no effect on that mediated by alpha(1)-AR. When alpha(1)-AR was irreversibly blocked and the activity of alpha(2)-AR remained intact, the contractile response mediated by alpha(2)-AR was no longer observed. The contractile response only reappeared in the presence of KCl of the threshold level, and the extent of the maximum contraction decreased, compared with control (with alpha(1)-AR being intact). The results show that there exists a functional alpha(2)-AR in rat aorta, however, the contractile effect of which depends on the stimulation of alpha(1)-AR.