Stimulation of the perivascular nerves elicited two types of electrical responses in the rat tail artery - excitatory junction potentials (e.j.p.s) and slow depolarization - and two types of mechanical responses - fast and slow contractions. Fast phasic contractions were triggered whenever action potentials were generated from either the e.j.p. or the slow depolarization reaching threshold. Slow tonic contractions and slow depolarization were sensitive to alpha-adrenergic blockade. However the slow contraction always preceded the slow depolarization. Bolus doses of exogenous noradrenaline also induced slow contraction and slow depolarization and the development of tension also preceded the membrane potential change. Increasing the external KCl also induced membrane depolarization however, contractions were not observed until the membrane was depolarized positive of -49 mV. In contrast, tension developed readily with membrane potential more negative than -49 mV with exogenous noradrenaline and neural stimulation, suggesting that the action of noradrenaline was not mediated by electromechanical coupling. It was concluded that vascular activity in the rat tail artery could be regulated by the e.j.p., the slow depolarization and also by pharmacomechanical coupling.