The rare earth elements Gd, Tb, Dy, Ho, and Er form compounds with Ge and Si at the 5 : 4 stoichiometry which have orthorhombic crystal structures. The suicides and germanides are in the same space group and have very similar lattice constants, but incomplete solid solubility in the system Gd5Si4Gd5Ge4 indicates that they are not isostructural. Magnetic measurements show that the suicides are ferromagnetic with relatively high ordering temperatures. The germanides are antiferromagnetic, but replacement of a small amount of Ge by Si in Gd5Ge4 produces solid solutions which are ferromagnetic at low temperatures and have intermediate transitions to antiferromagnetism before becoming paramagnetic. © 1967.