There has been a number of papers concerning relaxin. Relaxin is a nonsteroid and water-soluble ovarian hormone. Less attention has been paid to the third ovarian hormone than to steroids, namely, estrogen and progesterone. Our current knowledge of the hormone is yet incomplete. However, investigations so far made indicate that a more important role in reproductive physiology should be assigned to relaxin. It may be hard to understand throughly general phenomenon and mechanism of reproduction without knowledge of the hormone. Now, relaxin is under trial of its clinical use in women. In the field of animal prodnction, transference of fertilzed ova is in the stage of investigation now, and in the near future it will become a more important subject to be developed. However, the most troublesome technical neck supposed to be encountered in nonsurgical collection of ova is the neck of the uterus. And how to delate the cervical canal will become important. without solution of this problem, it seems to be difficult to realize the practical application of transference of ova in farm animals. Physiological function of relaxin seems to be favorable in removing the obstacles. It will for attainment of this object be repuired to use relaxin.