Aim The aim of this study was to evaluate the effect of psoriasis treatment on plasma concentrations of metalloproteinase-1 (MMP-1) and tissue inhibitor of metalloproteinases-1 (TIMP-1) with respect to disease severity. Methods MMP-1 and TIMP-1 were measured using an enzyme immunoassay in plasma of 32 patients before and after topical treatment. Data were analysed with respect to baseline values of the Psoriasis Area and Severity Index (PASI). Results Baseline plasma concentrations of both TIMP-1 and MMP-1 (1487 +/- 102 and 21.0 +/- 2.5 ng/mL, respectively) were significantly higher (P = 0.02 and 0.03, respectively) than normal. Both TIMP-1 and MMP-1 decreased significantly after completion of treatment to values similar to normal (1112 +/- 127 and 11.3 +/- 1.3 ng/ mL, respectively). There was a significant positive correlation (r = 0.522) between baseline PASI and TIMP-1 values. Significant differences were observed between baseline TIMP-1 concentrations in groups with PASI < 15 and PASI > 20. Baseline values (1697 162 ng/mL) in patients with severe course of the disease (PASI > 20) were significantly elevated in comparison to normal values. Treatment caused a decrease in TIMP-1 plasma concentrations in all groups, but a significant difference was noted only in patients with pretreatment PASI > 20. Baseline MMP-1 concentrations exceeded significantly normal values only in patients with PASI < 15 (27.2 +/- 6.3 ng/mL) and 15-20 (18.4 +/- 1.4 ng/mL). Treatment caused a significant decrease in MMP-1 values in all groups to levels similar to normal. Conclusions Our results confirm the role of TIMP-1 and MMP-1 in the pathogenesis of psoriasis. Pretreatment plasma TIMP-1 increased whereas MMP-1 decreased in patients with a more severe course of the disease. However, successful treatment causes normalization of these plasma protein concentrations irrespective of psoriasis baseline activity.