From a collection of 28 virulent phages peviously used for the typing of Rhizobium strains, four were selected for detailed characterization: 3C for R. trifolii, 3H for R. leguminosarum, 1A and 2A for R. meliloti, respctively. On the basis of their morphology phages 3H and 1A were included into group B and phage 3C into group C according to the classification of BRADLEY (1967). Rceptors for phage 3H were thermosensitive in contrast to those for phages 3C and 2A. Phage 3H kept in phosphate buffer (0.01 M), Na-citrate or EDTA, lost its activity. Ca++ and Mg++ protected the infectivity of phages 3H and 3C maintained in phosphate buffer.