The authors examined reaction of rhythm of the fetus heart in 32 pregnant women in the last month of pregnancy, after tone giving of 1000 and 2000 c/s and of intensity 100 db for 5 sec. The pulses of the mother and fetus were registered by Hellige's phonocardiograph before, during and after tone giving. Acceleration of fetus heart was observed in the group tested 1000 c/s average 7 beats a minute, in the group tested 2000 c/s 11 beats a minute. The mother's pulse did not show any acceleration during the tone or later on.