All polynomials considered in this paper belong to Q [x] and reducibility means reducibility over Q. It has been established by one of us [5] that every binomial in Q [x] has an irreducible factor which is either a binomial or a trinomial. He has further raised the question "Does there exist an absolute constant K such that every trinomial in Q [x] has a factor irreducible over Q which has at most K terms (i.e. K non-zero coefficients)?"A similar question could be asked for a quadrinomial, or, more generally, for a polynomial with m non-zero coefficients. This paper deals with the general problem, that could be formulated as follows:Given a positive integer m does there exist a number K such that every polynomial in Q [x] with m non-zero coefficients has a factor irreducible over Q with at most K non-zero coefficients (AT "terms")?If for a given m numbers K with the above property exist we denote by K{m) the least of them, otherwise we put K{m) = °°. We shall prove