Lichen planus (LP) is a chronic dermatosis whose clinical features include mildly erythematous to violaceous flat-topped, polygonal papules. The etiology of lichen planus is unknown, but it has been postulated that immune mechanism is important. Although it is of importance to monitor the course of immune-mediated diseases, there is a limited number of reliable biomarkers which can be used for lichen planus. Neopterin (NP), a 2-amino-4-hydroxy-(1'2'3'-trihydroxypropyl)-pteridine, is secreted by monocytes and macrophages, mainly as a response to INF-gamma secretion by activated T-lymphocytes. Therefore NP may be a sensitive marker of T-cell mediated immunity. The aim of the presented study was to assess the serum levels of neopterin in patients with lichen planus and to investigate whether serum neopterin levels reflect extensive lesions and progression of this disease. We studied 66 patients with lichen planus who were classified into one of two diagnostic groups: Group I comprised 33 patients with generalized lesions; group II comprised 33 patients with circumscribed lesions. The control group consisted of 30 healthy sex- and age-matched individuals. The serum neopterin concentrations were measured with a commercially available enzyme-linked immunosorbent assay kit. The results of our study are summarized in Table 1. In our study, the serum neopterin levels in the patients with lichen planus classified to group I (9.12 +/- 4.39 ng/mL) and group II (3.80 +/- 0.68 ng/mL) as well as in the whole collection of patients (group I and group II; 6.55 +/- 2.30 ng/mL) were significantly higher than those of the control subjects (2.55 +/- 0.34 ng/mL). Our findings confirm a role for enhanced cellular immunity as well as macrophages activation observed in lichen planus. It seems to us that evaluation of serum neopterin levels, despite the relatively low specificity, reflects extensive lesions and lichen planus progression.