Plasma levels of transforming growth factor (TGF)-beta1, tissue inhibitors of metalloproteinases (TIMP)-1, matrix metalloproteinase (MMP)-1 and interleukin (IL)-18 when analyzed separately demonstrate an association with psoriasis severity and treatment efficacy. To determine the highest correlation with the Psoriasis Area and Severity Index (PASI) score we carried out an analysis of these four proteins combined as the TTMI score. Concentrations of proteins were measured using an enzyme immunoassay in the plasma of 32 patients with chronic plaque-type psoriasis. The concentration of each biomarker was multiplied by the respective coefficient and the final individual TTMI score was the sum of these four values. TGF-beta1, TIMP-1 and IL-18 demonstrated significant positive correlation, whereas MMP-1 demonstrated significant negative correlation with the PASI score. The TTMI score calculated for individual patients varied from -79620 to 145713 (43050+/-8081) and demonstrated significant correlation with the PASI score. The lowest TTMI mean value was observed in patients with a PASI score <16 and the highest value was in patients with a PASI score >20. The combined measurement of plasma TGF-beta1, TIMP-1, MMP-1 and IL-18 has superior value as a biomarker of psoriasis activity in comparison with their separate analysis.