"Sometime before June 14, 1829, the Lord instructed Joseph Smith and Oliver Cowdery concerning their ordination as elders, which is a Melchizedek Priesthood office (HC 1:60-61). Furthermore, when Peter, James, and John appeared to Joseph and Oliver, they ordained them also as apostles ("D&C 27:12D&C 27:12) and committed to them "the keys of the kingdom, and of the dispensation of the fulness of times" ("D&C 128:20D&C 128:20; cf. 27:13)."

(Encyclopedia of Mormonism, 1-4 vols., edited by Daniel H. Ludlow (New York: Macmillan, 1992), 886, "Melchzedeck Priesthood")