 His relics were kept at Utrecht, and in 1421 and 1597 were examined at episcopal visitations.A large portion of his head is in the church of Saint Amelberga at Susteren, where an official recognition took place on 25 September 1885 under the supervision of the Bishop of Roermond [2].A letter written by Saint Lullus, Bishop of Mainz, to Saint Gregory is still extant [3].