BACKGROUND: Heat shock proteins (HSPs) are expressed by most living cells and play fundamental roles in many biological processes. Their synthesis increases by a variety of stresses in order to enable cellular survival. Although it is known that they play an important role in immune and inflammatory responses of the skin, the role of HSPs in the pathogenesis of skin diseases has been studied in only limited skin diseases. Lichen planus (LP) is a relatively common papulosquamous dermatosis, and cell-mediated immunity plays an important role in its pathogenesis. Although an altered expression of certain HSPs was reported in oral LP lesions, the expression of HSPs in cutaneous lesions of LP has not been investigated. In this immunohistochemical study, we aimed at investigating the role of HSPs in the pathogenesis of LP by studying whether there is any difference in HSP expression in cutaneous lesions of LP when compared to normal skin and psoriasis vulgaris (PV). METHODS: Formalin-fixed paraffin-embedded skin biopsy specimen blocks from LP patients (n = 39), patients with psoriasis (n = 20), and normal skin controls (n = 20) were used in the study. Antibodies to HSPs 60 and 70 were applied immunohistochemically by using streptavidin-biotin-horseradish peroxidase complex. An immunoreactivity intensity distribution index (IRIDI) was calculated to express the proportion of the immunoreactive cells as well as the staining intensity in different layers of the epidermis. RESULTS: The mean IRIDI scores for HSP60 expression in the basal, suprabasal, and superficial epidermal layers of cutaneous LP were moderately higher than those of normal skin, but not different from those of PV skin. These scores for HSP70 in lesions of LP were moderately lower than those for normal skin in the basal layer, but not significantly different from normal in the other two layers. Scores for HSP70 in PV lesions were markedly lower in all three layers. In the cells of the inflammatory infiltrates (mostly lymphocytes), HSP60 scores for LP were moderately higher, compared to those for PV, whereas scores for HSP70 were much lower for LP and very much lower for PV. CONCLUSIONS: Significantly altered levels of HSP proteins were found in cutaneous LP lesions in comparison with normal skin and psoriasis, suggesting the role of HSPs in the pathogenesis of LP.