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.