The present invention provides a drug delivery enhancer comprising, as an active ingredient, a substance that activates a lysophospholipid receptor, the enhancer being intended to be used for enhancing the delivery of a therapeutic drug for a disease involving abnormal blood vessel formation to an affected area； a pharmaceutical composition for treating a disease involving abnormal blood vessel formation, the composition comprising, as an active ingredient, a substance that activates a lysophospholipid receptor； and a method for screening for a therapeutic drug for a disease involving abnormal blood vessel formation, the method comprising selecting a substance that activates a lysophospholipid receptor specifically expressed in vascular endothelial cells of an affected area.
