The present invention provides a method for screening a compound or its salt that alters the binding property between MCH or its salt and SLC-1 or its salt, characterized by using MCH or its derivative or a salt thereof and SLC-1 or its salt is useful for screening an SLC-1 agonist which can be used not only as an appetite (eating) promoting agent but also as a prophylactic/therapeutic agent for weak pains, atonic bleeding, before and after expulsion, subinvolution of uterus, cesarean section, induced abortion, galactostasis, and the like, and an SLC-1 antagonist which can be used not only as an antiobestic agents (drug), an appetite (eating) modulator, and the like, but also as a prophylactic/therapeutic agent for hyperstimulation, ankylosing uterine contractions, fetal distress, uterine rupture, cervical laceration, preterm delivery, Prader-Wili syndrome and the like.