Psoriasis is a common chronic cutaneous disease affecting 1-3% of general population. Its pathogenesis is not fully understood, but the involvement of several cytokines has clearly been established. The aim of the present study was to evaluate serum concentrations of transforming growth factor (TGF)-beta 1 in patients with psoriasis vulgaris and to correlate these concentrations with severity of psoriasis and several other clinical parameters. Sixty patients with psoriasis and 38 healthy persons (control group) were included into the study. TGF-beta 1 was measured by enzyme-linked immunosorbent assay (ELISA) using commercially available kits. Serum concentrations of TGF-beta 1 in patients with psoriasis were significantly increased compared with the controls (42.9+/-9.9 vs. 37.7+/-6.0 ng/mL, respectively, p=0.004). Patients with more severe disease (PASI <24 points) had significantly higher serum concentration of TGF-beta 1 than those with mild psoriasis (PASI<24 points; p<0.001). Moreover, serum TGF-beta 1 concentration significantly correlated with disease severity (p=0.001). In patients with pre-existing infections of the respiratory tract, the concentrations of serum TGF-beta 1 were significantly decreased (p=0.03). Since serum concentrations of TGF-beta 1 are increased in patients with psoriasis, TGF-beta 1 might be used as a marker of psoriasis activity.