The effects of purinergic agonists on the mechanical and electrical activity of antral circular muscle of guinea-pig stomach were investigated. ATP potentiated the mechanical contraction without any change in membrane potential. To characterize the purinoceptors involved, effects of ATP analogues, especially P2X or P2Y receptor agonists, were studied. 2-MethylthioATP (2-MeSATP), a P2Y agonist, showed the same effects as that of ATP. On the other hand, a P2X agonists, alpha, beta-methyleneATP (alpha, beta-MeATP) incuced relaxation with hyperpolarization. At the holding potential of 0 mV, spontaneous transient outward currents (STOCs) were recorded in whole-cell mode. Externally applied ATP revealed transient increase of STOCs. Considering that STOCs reflect the changes of internal Ca2+, these results might be explained by the transient increase of internal Ca2+ release from internal Ca2+ store. From these results, it is concluded that there are at least two types of purinoceptors in guinea-pig stomach, and contractile response via P2Y-purinoceptor might be related to the elevation of internal Ca2+ released from internal Ca2+ store.