The flow of non-Newtonian purely viscous fluids through packed beds of different structures has been investigated and a model of calculation of the pressure drop is proposed. This model takes into account the structural parameters of the porous medium : the tortuosity tau, the dynamic specific surface area a(vd) and the porosity epsilon. This model has been verified experimentally for the flow of a power-law fluid through fixed beds of spherical particles, long cylinders and very flat plates. The present investigation covers a large range of Reynolds number including creeping and inertial flow regimes.