By means of macroscopic, histologic and enzyme histochemical methods the concept of Schuhmann and Wehler (1971) that the mature human placenta shows a morphological organization coincides with bloodflow-units was examined. The investigation deals with the existence and distribution of terminal villi which can be distinguished on the basis of histological and enzyme histochemical peculiarities. 90 placentas were available, 3 of which were premature. In 6 cases one half of the placenta or the whole organ was cut into serial sections. Mature placentas. Per dissected placenta on an average 6--7 regions with cavities in the intervillous space could be observed, which might correlate to the "placentones" postulated by Schuhmann and Wehler (1971). Using histological techniques at random scattered areas of different size of so-called "immature" villi exist in the near of the basal plate; a relation between these areas and the placentones cannot be seen. All enzymes investigated possess a lower activity in the syncytiotrophoblast of the immature villi than in the mature ones. The demonstration of phosphatases and lysosomal enzymes reveals groups of mature villi with increased activity; they form a patchy enzyme pattern. With the exception of dehydrogenases there is no relation between villi with special enzyme activities and the placentones. Premature placentas. The younger the placenta, the larger is the volume of immature villi. Result. At present a organization of the human placenta into morphological units which correlates to the bloodflow (placentones) cannot be seen. A principle of segmentation which bases on differences between the terminal villi cannot be demonstrated.