The present invention relates to a screening method for a compound or a salt thereof that alters the binding property of MCH or a salt thereof to SLT or a salt thereof, or a partial peptide thereof, an amide or an ester thereof, or a salt thereof, characterized by using MCH, a derivative or a salt thereof and SLT or a salt thereof, or a partial peptide thereof, an amide or an ester thereof, or a salt thereof. The screening method of the present invention is useful for screening an SLT agonist, which can be used as an agent for promoting appetite (eating), and an SLT antagonist, which can be used as a prophylactic and/or therapeutic agent for obesity.