In this paper a fully anisotropic symmetric weak formulation of Biot's equations for vibro‐acoustic modelling of porous elastic materials in the frequency domain is proposed. Starting from Biot's equations in their anisotropic form, a mixed displacement–pressure formulation is discussed in terms of Cartesian tensors. The anisotropic equation parameters appearing in the differential equations are derived from material parameters which are possible to determine through experimental testing or micro‐structural simulations of the fluid and the porous skeleton. Solutions are obtained by applying the finite element method to the proposed weak form and the results are verified against a weak displacement‐based formulation for a foam and plate combination. Copyright © 2010 John Wiley & Sons, Ltd.