Catalysts solid particles are supplied to a vertical reactor for the catalytic treatment of fluid charges, at the upper part of said reactor and are progressively withdrawn from the lower part thereof either continuously or periodically through a funnel having the shape of an inverted cone or an inverted pyramid. At least a portion of the charge is introduced at the lower part of the reactor through orifices above the walls of the funnel at a distance thereof from 1 to 500 times the average size of a catalyst particle.