From the study of the intermetallic compounds of YCo5, LaCo5, and PrCo5, it has been determined that these compounds crystallize in the hexagonal CaCu5structure. It has been reported that they have very high magnetocrystalline anisotropies and high saturation magnetizations. Especially, YCo5and PrCo5, compounds have higher saturation values and theoretical energy products than those of SmCo5. This experimental work is done with the intention of investigating: a) the magnetic properties of liquid phase sintered magnets of Sm1-xPrxCo5, and b) the change of X-ray diffraction patterns, lattice parameters, and magnetic properties of YCo5and LaCo5, during the liquid phase sintering process. For additional details, see Digests of the 1972 Intermag Conference (available from IEEE Headquarters).