Giorgio Mantica, Sandro Vaienti The Asymptotic Behaviour of the Fourier Transforms of Orthogonal Polynomials I: Mellin transform techniques (88K, latex) ABSTRACT. The Fourier transforms of orthogonal polynomials with respect to their own orthogonality measure defines the family of Fourier-Bessel functions. We study the asymptotic behaviour of these functions, and of their products, for large real values of the argument. By employing a Mellin analysis we construct a general framework to exhibit the relation of the asymptotic decay laws to certain dimensions of the orthogonality measure, that are defined via the divergence abscissas of suitable integrals. The unifying role of Mellin transform(s) techniques in deriving classical and new results is underlined.