The purpose of this study was to demonstrate the effects of silver spike point (SSP) low frequency electrical stimulation on plasma ${eta}-endorphin$ activities measured by radio- immunoassay from normal volunteer and the effects of ${eta}-endorphin$ on 5-hydroxytryptamine (5-HT, serotonin)-induced contraction investigated by isometric tension methode in rats. The current of 3 Hz continue type, but not 100 Hz continue type, of SSP low frequency electrical stimulation significantly increased in plasma ${eta}-endorphin$ from normal volunteer. The endothelial cell-dependent 5-HT-induced contractions were inhibited by ${eta}-endorphin$ $1{mu}M$. These results suggest that the ${eta}-endorphin$ regulates nociceptive-like substance, such as 5-HT, in part and that the SSP low frequency electrical stimulation, specifically current of low frequency of 3 Hz continue type, significantly increases plasma ${eta}-endorphin$ from normal volunteer.