Abstract. -Let F = (f 1 , . . . , fq) be a polynomial dominating map from C n to C q . We study the quotient T 1 (F ) of polynomial 1-forms that are exact along the generic fibres of F , by 1-forms of type dR + a i df i , where R, a 1 , . . . , aq are polynomials. We prove that T 1 (F ) is always a torsion C[t 1 , . . . , tq]-module. Then we determine under which conditions on F we have T 1 (F ) = 0. As an application, we study the behaviour of a class of algebraic (C p , +)-actions on C n , and determine in particular when these actions are trivial.