We prove that a finitely generated soluble group G is nilpotent-by-finite (respectively, finite-by-nilpotent) if every infinite subset of G contains two elements x,y generating a nilpotent-by-finite (respectively, finite-by-nilpotent)group.Moreover,for a positive integer k,if we suppose <x,y>is (nipotent of class k)-by-finite (respectively, finite-by-(nilpotent of class k)), then there is an integer c =c(k) such that G is (nilpotent of class c)-by-finite (respectively, finiteby-(nilpotent of class c)).