Temperature gradients similar to those existing in high-rated MX-type fuel [UC, (U,Pu)C and (U, Pu)C0.9 N0.1] have been obtained by heating cylindrical pellets with an alternating electrical current flowing in the axial direction. The power used and the heat impedance existing between the surface of the pellets and the cladding material is sufficient to produce average temperature gradients on the order of 150 kK/m in temperature regions between 1273 and 2273 K. Preliminary experiments show that under these temperature conditions, important restructuring of the MX-type fuel occurs after a comparatively short time (<40 h). Generally, four structural zones, characterized by a temperature and a temperature gradient, have been observed in cross sections of the heated specimens. In the direction of increasing pellet radius (decreasing temperature), one finds a zone with large rounded pores and large equiaxed grains, a zone where pores and grains are elongated in the direction of the temperature gradient, and next to this, a zone with intergranular pores and equiaxed grains, and, finally, an unrestructured zone at the edge of the pellet. Lenticular pores are not responsible for the fuel restructuring. They appear at temperatures around 1773 K, and their apparent migration rate is lower than that observed in uranium-plutonium oxides. The fuel heated in a thermal gradient also shows a general tendency to sinter at temperatures as low as 1523 K and a tendency to crack. The free volume created by the formation of cracks is independent of the initial density of the fuel. Plutonium enrichment at the open and healed cracks and at the surface of the pellets has been observed.