The influence of cross coupling terms in double porosity models for fractured reservoirs has been studied in this paper using numerical and perturbation methods. Attention is focused on the influence of the cross coupling coefficients on the transient solutions for the matrix and fissure pressures. Numerical simulations show that the addition of the cross coupling terms is equivalent to reducing the compressibility of the matrix block. A simple approximate solution is proposed for a quick estimation of the significance of the cross coupling effect in reservoir simulation, based on the solution of an uncoupled model.