The endometrium differs from all other tissues of the body in that it rhythmically changes its structure and function. For many years the meaning of these changes remained puzzling and obscure. At about the turn of the century some investi gators held the physiological fluctuations of the menstrual cycle to be inflamma tory changes. Later, when stricter criteria for the pathology of the endometrium were applied, morphologists misinterpreted pathological fluctuations in the cycle either as physiological variations, or they overlooked them entirely. Today as previously the pathologist is often confronted with the dilemma that he is unable to adequately diagnose the endometrium merely from the structural changes. Accordingly, the gynecologist finds the pathological report of little value. In like manner, if the clinical information given the pathologist is incomplete, then he cannot form a clear notion of the clinical problem. Although the detection of focal lesions of the endometrium is important, of much greater consequence is the recognition of functional (hormonally controlled) variations and their cyclic course, for it is from these that the clinician is guided in deciding what therapy he should use. The ability to detect such functional changes requires not only that the morphologist possess a thorough knowledge of the physiological and pathological anatomy of the endometrium but also that he receive exact information about the patient''s menstrual history and have in sight into clinical problems.
