AN EXPERIMENTAL study of the disorders of menstruation has been XJL in progress in our laboratory since 1929. The approach has been along two lines: 1) study of the changes in endometrial histology associated with abnormal uterine bleeding and 2) experimental production of abnormal menstruation in monkeys and direct observation of the associated vascular phenomena. Among other things, the study has demonstrated that menstrual disorders result from lesions in any of the endocrine glands or from constitutional disease secondarily affecting the endocrine system. The primary lesion operates through the ovaries to produce the menstrual symptom. The degree of ovarian involvement is indicated by the endometrial histology. There is no constant correlation between the type of menstrual abnormality and the severity of the ovarian dysfunction as indicated by the endometrium (Burch and collaborators, 1937; 1942 (1, 2)). The study of endometrial vascular phenomena was undertaken in the hope of clarifying the question of the relationship of the bleeding abnormalities to ovarian failure. This report is one of a series dealing with various aspects of the study.