1. Several kinds of apparatus for measuring the comparative frequency responses of phonendoscopes are described in the article. 2. With the apparatus described it is possible to check (by the comparison method) the frequency transmission response of the entire acoustic channel in a phonendoscope. 3. The reproducibility of the measurements with time and for a complete repositioning cycle on the measuring apparatus is adequate. 4. The information obtained from a recording of the frequency transmission responses on phonendoscopes not only permits the existence of defects to be detected, but also their type. 5. The apparatus described should prove useful to industrial enterprises that manufacture phonendoscopes for checking their output parameters. In concluding the authors express their appreciation to Prof. N. N. Savitskii, Member of the Academy of Medical Sciences of the USSR, to Dr. M. S. Kushakovskii, M. D., to Asst. Prof. R. I. Gismatullina, and also to I. M. Kitvaka, engineer, for a number of valuable consultations on the creation of this apparatus.