1. In the preparation of sponge iron by the composite method, reduction is governed by a predominantly diffusion-type mechanism, i.e., obeys an essentially parabolic law, when a loose charge is used; with a briquetted charge, a kinetic mechanism becomes operative, in consequence of which reduction is governed by a linear law. 2. The productivity of reduction furnaces is strongly affected by the specific weight of the charge held in the trays. By decreasing the specific weight from 7.5 to 5.5 g/cm2 and reducing the tray-pushing and reduction times from 17.5 to 9 min and from 315 to 170 min, respectively, it is possible to increase the productivity of the Brovary Powder Metallurgy Factory reduction furnaces in loose charge reduction by 35% compared with the present level.