The enrichment of high field strength elements (HFSE) in Sulu Arc lavas has been proposed as a product of metasomatism of the mantle wedge. It is postulated that a dacitic melt, derived from melting of subducted Sulu Sea basaltic crust, stabilizes in the mantle wedge amphibole, which later breaks down and releases HFSEs into the source of basaltic arc lavas. New data for primitive, high-K calc-alkalic basalts that contain the highest HFSEs among Sulu Arc lavas and seafloor basalts subducting along the Sulu Trench have contrasting chemical and isotopic characteristics. This makes it unlikely that the source of HFSE enrichment in Sulu Arc lavas is melt derived from the subducted Sulu Sea basaltic crust or amphibole formed during metasomatism of the mantle wedge by such melt. We propose that HFSE enrichment in Sulu Arc lavas results from melting of a geochemically enriched component in the mantle wedge.