Ferromagnetic interactions of the rare earth elements in dilute solutions or in compounds with non-magneticelements have been discovered and will be described. The Curie points are essentially proportionalto the spin while the saturation moment follows the value for the effective moment. This ferromagneticinteraction, known to take place via the conduction electrons, follows criteria resembling closely those forthe occurrence of superconductivity.It is shown that by suitable combination of similar superconductors and ferromagnets both phenomenacan happen simultaneously in the same crystal.