The responses of prolactin (PRL) and oxytocin (OT) to suckling and breast massage were examined in lactating women. The suckling group showed increase in frequency of pulsatile release of OT and increase of the plasma PRL level. In contrast, the breast massage group showed a significant, but not a pulsatile increase in the plasma OT level and no increase in the plasma PRL level. These findings suggest that suckling causes both milk production and milk ejection, while breast massage causes only ejection of milk already stored in acini, and that prolactin release is not related to increase of the oxytocin level itself, but to its pulsatile release.