[en] Phase equilibria in the systems GdI₃-CeI₃-H₂O and GdI₃x5CO(NH₂)₂-H₂O are studied at 0 deg C using the isothermal method. In both cases formation of solid solutions of the I type according to the Rosebom classification is established. Using the data on solubility and the theory of regular solutions over the whole concentration range complete enthalpies of solid solution formations in each system are calculated