Prostaglandin(PG) is ubiquitously distributed in most mammalian tissue and their actions are complicated. Especially in autonomic nervous system, there are evidences indicating that PGs act as neuromodulators i.e., PGs, which are released in the vicinity of autonomic neuroeffector junctions, influence the release and the response of the neurotransmitter. Present study was undertaken to elucidate the interrelationship between PGE_2α and adrenergic α₂-receptor function in electrical field stimulation induced contractile response of vas deferens in rat. Male rat, weighing 150 ~ 200 g, was sacrificed and vas deferens was obtained. The isolated vas deferens strip was placed between two platinum electrodes in temperature controlled (37˚C) muscle chamber containing Tyrode s solution and the electrical field stimulation(EFS) induced contraction was recorded with Grass Polygraph(Model 7) via force displacement transducer (FT .03, Grass). The results are summarized as follows: 1) Electrical field stimulation for 1sec( 1 msec, 40 cps) induced contraction of vas deferens was completely blocked by tetrodotoxin. 2) Bretylium caused marked inhibition of the EFS-induced contraction, hut tyramine and cocaine augmented the contraction. 3) EFS-induced contraction was inhibited or little affected in distal portion of vas deferens by norepinephrine or methoxamine, but the contraction was rather augmented by the α-agonists in proximal portion. 4) Clonidine inhibited the EFS-induced contraction proportionally to the concentration in distal portion, which was blocked by yohimbine pretreatment, but in the presence of PGE_2α the blockade by yohimbine was reversed. 5) Indomethacin pretreatment reduced the effect of clonidine, but addition of PGE_2α after washing-out the indomethacin caused the contraction to the control level. From these results it is suggested that PG synthesis is a necessary step and the PG itself has a permissive role in α₂-adrenoceptor action in rat vas deferens.