By means of scanning electron-microscopic investigations, thorn-like projections (TLP) were observed in the cilio-secretory epithelium of the ventral surface of the human endo-cervix. These projections, which seem to be characteristic of a new cell type, were seen at different stages of the menstrual cycle (days 8, 14 and 21) in 4 apparently healthy fertile women. Striking differences in length, with a maximum size at midcycle, suggest an evolutive process throughout the menstrual cycle. The origin and possible physiological role of TLP in the reproductive process are discussed.