To Professor W. M. Schmidt on his 60th birthday 1. Introduction. Denote by |P | the length of a polynomial P ∈ Z[x], i.e. the sum of the absolute values of the coefficients of P . The purpose of this paper is to investigate the irreducibility of non-constant neighbouring polynomials over Q. Here we say that two polynomials with integer coefficients are neighbouring if their difference is of relatively small length and small degree. By means of Eisenstein's irreducibility theorem it is easy to show that for given P ∈ Z