The formation of Pb3MgNb2O9 (PMN) perovskite by the reaction of PbO with columbite type MgNb2O6 precursor as well as Mg(OH)(2) with Pb3Nb2O8 precursor is investigated. It has been shown that pure PMN perovskite can be made by reacting PbO with phase-pure MgNb2O6 at about 700 degrees C without adding excess MgO or PbO. Evidence for the formation of an intermediate Mg-containing pyrochlore phase, which coexists with PMN perovskite, is found when this reaction is carried out at low temperatures (500-650 degrees C). In contrast, no significant reaction has been observed when Pb3Nb2O8 is reacted with Mg(OH)(2) between 500 and 675 degrees C, suggesting that the activation energy for the reaction between PbO and MgNb2O6 to form the PMN pyrochlore/perovskite phase is less than that for the reaction of MgO with Pb3Nb2O8.