Matrix metalloproteinases belong to a growing family of proteases controlled by specific tissue inhibitors, involved in tissutal flogosis, wound healing, cancer invasion and metastasis. We developed an in vitro model to screen for potential toxic compounds in professional exposure. Human keratinocytes (HaCat) were used as target cells while matrix metalloproteinases (MMP) were selected as responders, developing and in vitro model of allergic dermatitis. The chemical agents: potassium dichromate and nickel sulphate as positive teste, because represent the main etiological agents of allergic dermatitis. Nickel contact at very low concentrations (10(-5), 10(-6) M) induced upregulation of MMP-2 and IL-8 mRNA production; chromium contact at very low concentrations killed all cells. Actually, our in vitro research is based on analysis of cytotoxic effects of xenobiotics on human lung fibroblasts; simultaneously we verified serum increasing in vivo of MMP-9, determinated in workers serum, exposed to anesthetic gas (fluorane). In only six exposed workers we observed MMP9 increasing over than normal range. Actually, we are continuing our research on a more representative sample.