Many investigators have reported proliferation of terminal cutaneous nerves and upregulation of various neuropeptides (substance P; vasoactive intestinal polypeptide; calcitonin gene-related peptide) in psoriatic lesions. Nerve growth factor promotes growth of nerves and causes upregulation of neuropeptides like substance P and calcitonin gene-related peptide. In this study we investigated the expression of nerve growth factor in psoriatic lesions; non-lesional psoriatic skin; lichen planus and normal control skin. Immunoperoxidase staining was applied on cryosections prepared from snap-frozen biopsy specimens. The primary antibody used was a polyclonal anti-NGF-beta antibody. Nerve growth factor was detected only in the keratinocytes. In psoriatic tissue the number of keratinocytes per square millimeter of epidermis positive for nerve growth factor was 84.7+/-46.3 compared to 44.8+/-29.9; 18.9+/-11.8 and 7.5+/-16.9; respectively; in non-lesional psoriatic skin; normal skin and lichen planus. Increased expression of nerve growth factor substantiates larger numbers of terminal cutaneous nerves and upregulations of substance P and calcitonin gene-related peptide in psoriatic lesions. In addition; nerve growth factor is mitogenic to keratinocytes; activates T-lymphocytes and can induce migration of inflammatory cellular infiltrates; histological features characteristic of psoriasis.