The authors report a detailed histologic study of the process of replacement of solitary vellus hairs by solitary coarse hairs in the axilla. The replacement process is revealed to be quite different from the ordinary hair cycle. In puberty, hormonal activity causes the vellus hair follicle to become multilobular. The vellus hair expires, and formation of a new bud and a new (coarse) hair begins to develop from the upper isthmal portion of the follicle just below the sebaceous duct. The new hair pegs downward, until the formation of a new hair bulb (matrix) is completed, and then grows upward as a coarse terminal hair.