The cell cycle of cultured human endometrial adenocarcinoma cells were observed with a SEM using the synchronous culture method and the following results were obtained. In the M phase, the cells changed morphologically to become a minimum size and rounded in shape. Filopodia became thin and straight and reached their maximum length. Moreover, blebs reaches their greatest number. In the G0+1 phase, the cells developed from a round shape to an oval shape, and finally became polymorphic. The ends of the filopodia degenerated and became shortened. The number of blebs was decreased only in this stage. During the S phase, the cells became slender and reached maximum size. Short filopodia reappeared. No blebs but the largest microvilli were found. When we compared the late G1 with the early G2 phase, we found polymorphism of the cells and coexistence of microvilli and blebs common to both phases. However, ruffles were observed only in the former phase, while in the latter phase renewal of short filopodia together with thick and bent filopodia was evident. When we compared the late G2 with the early G1 phase, we found that the cells were small in size and round shape, and that the existence of blebs was common to both phases. However, the tips of the filopodia were destroyed in the latter phase, while in the former phase thick and bent filopodia were observed.