Collagenolytic activity (CA) in cervical fluid of patients with inflammation of periodontium was increased with increasing activity of the pathological process. Enhanced CA in patients with severe forms of periodontitis is probably due to depletion of endogenous inhibitors and to the transition of the latent collagenase to its active form. Studies of the effect of EDTA, PMSF and PCMB on CA show that proteinases are an essential factor in inflammation of periodontium.