The solid-liquid wetting factor, f, was experimentally determined in a fixed-bed three-phase reactor with downward concurrent gas and liquid flows (trickle-bed reactor). The method employed consisted of comparing the shear stress obtained when two phases (liquid and gas) circulated through the bed, with that obtained at liquid-full bed conditions, maintaining the intrinsic liquid and gas velocities constant. The shear stresses were related with pressure drop and liquid hold-up. In this way, a non-intrusive method can be applied to any chemical trickle-bed reactor by only measuring pressure drop and liquid hold-up. Experiments were carried out in a pilot unit, where the flow of both phases was modified, obtaining a direct dependency off with the flow and hold-up of liquid and f values in agreement with those reported by other methods.