A virus that lysed its homologous culture was obtained in 20 out of 29 attempts by inoculating wheat with different cultures ofXanthomonas trifolii. Each virus lysed, in addition, certain but in no case all other cultures. A composite virus-filtrate lysed all 29 cultures and 157 of 191 additional isolates obtained from various kinds of cultivated seeds. It did not lyse any of the 18 cultures ofX.translucensnor any of 17 other recognized species or subspecies.