van Diejen, JF (van Diejen, J. F.1; Emsiz, E (Emsiz, E.). Univ Talca, Inst Matemat & Fis, Talca, ChileWe present explicit Pieri formulas for Macdonald's spherical functions (or generalized Hall-Littlewood polynomials associated with root systems) and their q-deformation the Macdonald polynomials. For the root systems of type A, our Pieri formulas recover the well-known Pieri formulas for the Hall-Littlewood and Macdonald symmetric functions due to Morris and Macdonald as special cases