Tumor associated proteolysis is an essential mechanism in invasion and metastasis of cancer. The influence of the serine protease urokinase-like plasminogen activator (u-PA) and its inhibitor plasminogen activator inhibitor-1 (PAI-1) on the clinical prognosis of squamous carcinoma of the head and neck region (HNSCC) was evaluated. U-PA and PAI-1 levels were measured in tumor biopsies of 41 HNSCC patients and 6 biopsies of healthy oral mucosa using ELISA technique. Patients were followed for an average of 24 months. U-PA concentration in tumor tissue was four times higher than in healthy mucosa (4.96 ng/mg protein versus 1.32 ng/mg). PAI-1 levels were 22 times higher (69.55 ng/mg versus 3.18 ng/mg). Univariate Cox regression analysis revealed significant correlation (p=0.022) of PAI-1 with recurrence of the disease and no significance for u-PA. PAI-1 might become a new functional risk factor reflecting clinical prognosis.