Human hair follicles were grafted onto 2 strains of immunodeficient mice to compare the regeneration potential of vellus (miniaturized, balding) and terminal (hairy, nonbalding) follicles from males and a female exhibiting pattern baldness. Each mouse had transplants of both types of follicles from a single donor for direct comparison. Grafted follicles from 2 male donors resulted in nonsignificant differences in mean length (52 mm vs 54 mm) and mean diameter (99 μm vs 93 μm) at 22 weeks for hairs originating from balding and hairy scalp, respectively, corresponding to 400% versus 62% of the mean pretransplantation diameters. Follicles from the female donor transplanted to several mice also resulted in nonsignificant differences in length (43 mm vs 37 mm) for hairs from balding and hairy scalp, respectively, during a period of 22 weeks. The mean diameter of the originally vellus hairs increased 3-fold, whereas the terminal hairs plateaued at approximately 50% of pretransplantation diameter, resulting in a final balding hair volume double that of the nonbalding hairs. This report shows that miniaturized hair follicles of pattern alopecia can quickly regenerate once removed from the human scalp and can grow as well as or better than terminal follicles from the same individual. (J Am Acad Dermatol 2003;48:752-9.)