Genital bleeding as a main symptome of myoma of the uterus is not uncommonly encountered by gynecologist. Clinical and histological studies were carried on both entdometria and ovaries of 24 patients with myoma of the uterus. Specific attention was paid to clarify the bleeding mechanism from this diease, using histological and transparently modeled specimens of the blood vessels. The transparent specimens were made as follows. After hysterectomy was done, a pigment solution was injected into the vessels and then, after an adequate dehydration, the specimens were trausferred to methylsalcilate for immersion. The binocular stereomicroscope was used for the present study. Results of the study are summarized in the following. 1) Menstrual abnormality was found in 70,9% of all the cases. 2) The endometrial and ovarian histology has the same cyclic changes as the normal does, and the endometrial secretory phase is compatible with the corpus luteam in the ovary. 3) The majority of cases showed endometrial hyperplasia. 4) In case of submucous myomata, a striking difference of the endometrial thickness and the histologic pictures between the surface endometria above the myomata and the other areas. 5) The blood vessels of myomatous endometria have the same cycle as those of the normal do. Although the intramuscular blood vessels in influenced by the myomata mass, there is no specific morphological changes found in the endometrial blood vessels. 6) In this study, no venous sinus was observed in the endometrium. 7) It would appear that the menstrual abnormality under myoma of the uterus may be caused by the mechanical effect from the myomatous mass upon the endometrial and myometrial vessels.