Although some increased enzyme activities in PMN leukocytes isolated from the circulation of psoriatic patients have been previously described, none of these enzymes had been studied in plasma for determination of disease activity. The purpose of this study was to evaluate whether plasma PMN elastase levels might be a good marker for determination of disease activity of psoriatic patients. Plasma PMN elastase and some acute phase reactants including alpha-1 antitrypsin, alpha-2 macroglobulin, fibrinogen, erythrocyte sedimentation rate(ESR), and transferrin were studied in thirty-nine patients with psoriasis, including 16 controlled patients, and forty healthy control subjects. PMN elastase and the acute phase reactants except transferrin were found to be significantly higher in the psoriatic patients than in control subjects. The PMN elastase level in the patients was about 6-fold higher than that of the control group. The PMN elastase levels in the patients in the inactive period was two-fold higher than in the control subjects. PMN elastase was found to correlate significantly with PMN leukocyte count and alpha-1 antitrypsin in active and inactive periods of the disease, but with fibrinogen and psoriasis area and severity index (PASI) only in the active period of the disease. We conclude that plasma PMN elastase level may be a more specific and sensitive inflammatory marker than alpha-1 antitrypsin, alpha-2 macroglobulin, ESR, and may be a good marker for diagnosis and follow up of the disease activity of the psoriatic patients. (C) 1997 Elsevier Science B.V.