Several cytokines have been shown to be increased in psoriasis, mainly at the local and sometimes at the systemic level. At present, no data concerning the relationships between psoriasis and interleukin-7 (IL-7) are available. This biological modifier regulates immune response by means of its pleomorphic activities, including the ability to stimulate different monocyte functions, such as killing of intracellular pathogens, induction of cytokines, and enhancement of some membrane molecule expression. Study groups consisted of nine psoriatic and nine normal subjects. Using a commercially available immune-enzyme method, IL-7 concentrations were determined in various samples: biopsy and scale extracts, peripheral blood mononuclear cells (PBMCs) supernatants, and sera. The results show that IL-7 levels are significantly increased both in biopsy and in scale extracts obtained from lesional skin compared to those obtained from nonlesional and normal skin (P at least < 0.01). In addition, the serum values were higher in psoriatic patients than in the controls (P = 0.003). In contrast, no significant differences were observed in the supernatants of unstimulated PBMCs maintained in culture for 48 hr. These data suggest that IL-7 is involved in some way in the pathomechanisms of psoriasis and that the keratinocyte may be a candidate for psoriatic IL-7 overproduction.