Site-specific restriction endonuclease BbrI has been found in bacteriophage resistant strain B. bronchioseptica 4994. The technique was elaborated for purification of BbrI to the stage free of nuclease and phosphatase contamination. The yield of purified enzyme is 6000-20 000 units per 10 g of biomass. BbrI recognises and cleaves the same DNA sequence as HindIII with the formation of four-nucleotide cohesive ends. The simplicity of cultivation, security for human, presence of the single restriction endonuclease and the high level of its production make B. bronchioseptica 4994 a promising producer of BbrI restriction endonuclease, isoshizomeric to HindIII, for use in experimental practice in industry.