Nerve growth factor (NGF) and its high affinity receptor, tyrosine kinase A (TrkA)   are essential for nervous system development.  Recently,   it has been shown that these members of the neurotrophin family are also involved in murine hair morphogenesis and     cycling. However,   it   remains    to   be elucidated   whether   NGF   and other neurotrophins   play   any role in human skin and hair biology. As a first step towards this end,  the  irnmunoreactivity (IR)  of  NGF   and  TrkA  was studied in human scalp  skin and hair  follicles  (HF)   in  situ   by immunofluorescent   and   light microscopic  immunohistology. Both NGF and TrkA showed prominent, yet distinct IR patterns in human scalp anagen hair follicle (anagenYI),whereas they were weakly expressed or absolutely absent from catagen and telogen hair follicles. Within hair follicle compartment, NGF IR was prominent in the outer root sheath (ORS), dermal papilla (DP), connective tissue sheath (CTS)   and   inner   root sheath (IFS). Td~A IR was prominent only in the ORS of the anagen HF. Outside from the hair follicle compartment, both NGF and TrkA showed prominent IR tn   the epidermis, sebaceous gland and sweat gland. These observations provide the first indication  that  NGF  and TrkA are  expressed in  human  scalp skin and Hf, and suggest that TrkA -mediated signalling plays a role  not only in murine, but also in HF biology, and promise prospective therapeutic in the treatment of hair cycle and skin-related disorders.