The aryl hydrocarbon receptor (AhR) is highly expressed in psoriasis skin lesions. The aim of this study was to investigate serum concentrations of AhR, cytochromes P450 (CYP) 1A1 and 1B1 in patients with exacerbated psoriasis vulgaris treated with combined therapy of ultraviolet radiation (UVR) and crude coal tar. The analyses were performed by using enzyme-linked immunosorbent assays. Before the treatment, the patients had significantly higher serum levels of AhR and CYP1A1 than healthy controls. AhR median noticeably decreased after the therapy; nevertheless, it remained significantly higher compared to the controls. CYP1A1 levels measured before and after the therapy did not differ significantly. Serum CYP1A1 positively correlated with AhR values before and after the treatment. The serum values of CYP1B1 were very low and we did not see any differences between the study group and the control group. The study demonstrated that serum levels of AhR and CYP1A1 could indicate their immunopathological and metabolic roles in exacerbated psoriasis. and Corresponding author: Martin Beránek