127 specimens, obtained by different methods from the myometrium and the placental bed after parturition, are investigated histologically. This material includes normal pregnancies as well as cases of maternal diabetes with and without hypertension and cases of hypertension in EPH-gestosis. The different parts of the arterial system (spiral arteries, basal arteries, radial arteries) are separately investigated. Physiologically, the pregnancy induces changes in the wall of the decidual arteries and possibly in the distal part of the radial arteries. The fibromuscular layer including the elastic fibers were destructed and replaced by fibrin and connective tissue. For this reason, in these parts of arteries it is very difficult to separate pathological from physiological changes. Maternal hypertension produces in myometrial, basal and decidual arteries (myometrial part) a thickening of the arterial wall. This thickening is caused in arteries with normal structure by hypertrophy of the media, in the spiral arteries by intimal processes (edematous reaction of the intima, deposition of foam cells) and fibrinoid necrosis of the arterial wall. The cases of maternal diabetes without hypertension are characterized by an increase of fibrin deposits in the wall of the distal part of the spiral artery. In the proximal part of the spiral artery we have found in two cases without hypertension some foam cells in the wall. Myometrial arteries show particularly thickening of the wall and narrowing of the arterial lumen, less frequently intimal swelling and groups of foam cells. In diabetes mellitus, complicated by hypertension, we could find changes in the proximal part of the spiral artery and in the basal arteries. This alterations correspond with the changes in cases of hypertension without diabetes. In the myometrial arteries the pathological processes are the same as in cases of diabetes without hypertension. A significant increase of pathological processes by the diabetes mellitus alone exists only in the myometrial arteries. Besides, in the small arterial vessels of the myometrium in diabetes occurs a proliferative angiolopathy, involving cases of White classes D and F only. We could demonstrate the so-called ‘acute atherosis’ in a small number of cases in the myometrial part of the spiral artery and in the distal part of the radial artery, too. It concerns especially cases of maternal hypertension, more seldom cases of normal pregnancy and diabetic pregnancy without hypertension.