Changes in the electrical resistance of some powdered substances during compaction have been studied. Two limiting states were introduced for the description of the powder-column resistance : in the first state it equals the resistivity of the solid phase; in the second its resistance equals zero. Contacts between particles forming the conducting cross-section were expressed as a function of the powder column height. Two mechanisms for the change of the column height were proposed : (a) shifting of particles; (b) particle deformation. The dependence of the resistance on the height of the powder column and on its conducting cross-section was mathematically described. The validity of the equations was experimentally verified using carbonaceous substances with different conductivities. Special enamel was used as an insulating liner, which enabled measurements to be made at pressures of up to 1500 MPa.