The relationships between hair loss, hair growth, and vascular supply in the human scalp have not been precisely delineated. Alopecias from severe inflammatory processes which destroy the follicular unit have been fully documented. The combination of genetic susceptibility and androgenic inhibition of follicular growth in male and female patterned baldness is well recognized, but the role played by the vascular system is unknown. Little is understood concerning the pathogenesis of the mildly inflammatory alopecias, exemplified by alopecia areata, alopecia totalis, and pseudopelade of Brocq. Chronic diffuse thinning of the hair in women in the absence of known hereditary factors, while apparently becoming increasingly common, has not been satisfactorily explained. In a recent study, Kligman1 has shown that temporary thinning of scalp hair following severe fevers, infections, pregnancy, and heparin administration is due to accelerated production of normal telogen hairs. The causative mechanisms in this group likewise remain obscure. This