BACKGROUND Lichen planus together with its oral variant is a chronic, inflammatory disease of the skin and the mucosa of unclear aetiology and with an unpredictable course that still poses a major problem in terms of diagnosis and treatment. The objective of this study was to assess the concentrations of interleukin-6 (IL-6) and neopterin in saliva and serum of patients with lichen planus (including reticular and erosive form of oral lichen planus) and to compare them with the concentrations observed in healthy controls. METHODS The study material comprised serum and saliva samples from 56 patients diagnosed with lichen planus and 56 healthy volunteers. The ELISA test was used to measure concentrations of IL-6 and neopterin in the serum and saliva of the study participants. RESULTS The concentrations of IL-6 in saliva and serum of patients with lichen planus were significantly higher than in controls (P = 0.0002; P < 0.0001). The difference remains significant after adjustment for gingivitis and age. Patients with atrophic-erosive oral lichen planus had significantly higher IL-6 concentrations in their saliva compared to patients with reticular form of disease (P = 0.01). The concentrations of neopterin were significantly higher in the serum but not in saliva of lichen planus patients vs. controls (P <0.0001). CONCLUSIONS Serum levels of proinflammatory cytokines IL-6 and neopterin are increased in lichen planus as well as the salivary concentrations of IL-6. The differences observed in IL-6 levels in patients with erosive-atrophic forms of oral lichen planus may indicate a substantial role played by the cytokine in the disease.