Studies aimed at improvement of the technique for isolation of B. fragilis from the pathologic material and for identification thereof were carried out. Methods of anaerobe indication in bacterial associations (the disk and screening techniques) were used for the detection and isolation of B. fragilis. Use of these methods has facilitated and accelerated the agent isolation. Basing on the literature data and his own findings on the isolation rate of B. fragilis and on the incidence rate of differential signs, the author has calculated the diagnostic coefficients and informative value of each test. Use of these coefficients helped make the identification of these agents more reliable and in a number of cases permitted reducing the number of signs to be detected for the identification.