Comparative studies of pathological anatomy of intrauterine mycoplasmosis of man and cattle were carried out. On the basis of investigations of 22 deceased newborns and of 3 stillborns with uterine infection caused by Mycoplasma pneumonia descriptions of lesions of various organs are presented. They most regularly were defected in the liver. In the respiratory organs in this infection, in contrast to respiratory mycoplasmosis, lesions of respiratory departments, not of the respiratory tract, were predominantly observed. The investigation of 18 liveborn and 5 stillborn calfs with intrauterine infection caused by Mycoplasma bovirhinis revealed the same regularities of the pathological process. The localisation of lesions and the presence of changes in the placenta justify the conclusion that the disease developed, as a rule, as a result of hematogenic transplacental infection.