Disclosed herein is a method for inhibiting the premature polymerization of ethylenically unsaturated monomers comprising adding to said monomers an effective amount of: A) at least one nitroxyl compound, and B) at least one quinone alkide compound having an electron-withdrawing group at the 7-position. Additionally, a composition is disclosed that comprises: A) at least one nitroxyl compound, and B) at least one quinone alkide compound having an electron-withdrawing group at the 7-position.