The alloying behaviour shown by the rare earth metals (R) with different elements in the Periodic Table is summarized. Special attention is given to the trend of the Δ f o r m H and the experimental values are compared with those obtained according to Miedema. Examples of the trends observed for different properties and for the Δ f o r m H are then reported by comparing the results obtained in a series of R-Me systems of a given element Me with different rare earth metals. The special behaviour of Eu and Yb in comparison with that of the normal trivalent R is summarized. The interest of the mentioned behaviour in assessing and evaluation procedures is exemplified. A short summary of the results recently obtained in our laboratory in the thermochemical investigation of a number of R-Me systems is presented.Dans cette etude sont resumes certains aspects du comportement des alliages de terres rares (R) avec les elements (Me) de la classification periodique. En particulier nous avons pris en consideration les valeurs experimentales de l'enthalpie de formation des alliages (Δ f o r m H) et la comparaison avec les valeurs calculees a l'aide du modele semi-empirique de Miedema. L'allure de la fonction enthalpie (Δ f o r m H) ainsi que les differentes proprietes des alliages R-Me ont aussi ete discutees. Nous avons mis en evidence le comportement different des elements Eu et Yb par rapport aux autres terres rares trivalentes. Un resume des recents resultats thermodynamiques obtenus au laboratoire, pour un certain nombre d'alliages R-Me, est presente.