+ et Tm3 + dans les propriétés magnétiques et les propriétés de transport, le fait d'obtenir ces résultats aussi bien dans la limite diluée à une impureté que dans TmSe stœchio métrique, nous amène à conclure que tous les sites de thulium sont équivalents. — TmSe exhibits both non integral valence and antiferromagnetic order in contrast to most other intermediate valence systems which are non magnetic at low temperatures. We report on measurements of lattice constant, magnetic susceptibility and resistivity made on single crystals of Tm^Se over its range of solid solubility, 0.79 ^ x ;g 1. We find direct correlations among the physical properties, valence and concentration. The fraction of divalent character in TmxSe increases with x, the most Tm deficient sample being essentially trivalent. Alloys of TmSe with YSe have also been prepared as single crystals. Lattice constants and susceptibilities indicate that these materials have non integral valence over the entire system. With increasing Tm concentration a metallic Kondo resistivity changes smoothly towards the high resistivity characteristic of stoichiometric TmSe. Although we find the properties of Tmz+ and Tm3+ configurations in magnetic and transport measurements, since these results are observed in both stoichiometric TmSe and in the dilute single impurity limit, we conclude that all TmSe sites are equivalent.