Abstract. We define non-holomorphic Poincaré series of exponential type for symplectic groups Sp m (R) and continue them analytically in case m = 2 for the small weight (4, 4). For this we construct certain Casimir operators and study the spectral properties of their resolvents on L 2 (Γ\ Sp 2 (R)). Using the holomorphically continued Poincaré series, the holomorphic projection is described in terms of Fourier coefficients using Sturm's operator.