We present a convenient synthesis of a chemical library of lactam-fused β-carbolines via a Ugi four-center three-component reaction employing [1-formyl-3-(methoxycarbonyl)-9H-pyrido[3,4-b]indol-9-yl]acetic acid or (1-formyl-9H-pyrido[3,4-b]indol-9-yl)acetic acid, amines and isonitriles.