A phage specific for one isolate of Xanthomonas translucens f. sp. undulosa and three polyvirulent phages active against various members of the X. translucens group have been isolated. One of the polyvirulent phages, Pg35, lysed 24 out of 28 isolates of X. translucens; the other two were somewhat less active. Attempts to use form specific phages to identify cultures of X. translucens f. spp. hordei, hordei-avenae, and undulosa were unsuccessful. However, use of a phage specific for f. sp. secalis to detect homologous cultures gave encouraging results.