The profile of salivary proteases and their cellular origin, with special reference to polymorphonuclear leukocytes and bacteria, was studied in localized juvenile periodontitis and compared with adult periodontitis and healthy controls. General proteolytic activity in saliva as well as collagenase, elastase-like and trypsin-like activity was measured. In addition, the sensitivity of salivary collagenase of patients with localized juvenile periodontitis to doxycycline inhibition was studied. The saliva of localized juvenile periodontitis patients contained low amounts of collagenase compared with adult periodontitis saliva, and almost all salivary collagenase was found to exist in endogenously active form, as was found to be the case also in adult periodontitis patients and healthy controls. The salivary collagenase of localized juvenile periodontitis patients was relatively insensitive to 100 mumol/l doxycycline but was completely inhibited by 600 mumol/l doxycycline, reflecting rather matrix metalloproteinase-1 (fibroblast-type) than matrix metalloproteinase-8 (polymorphonuclear leukocyte) enzyme. The saliva of localized juvenile periodontitis patients also contained low amounts of elastase-like activity compared with the saliva of untreated adult periodontitis patients. Scaling and root planing caused a significant decrease in elastase-like activity in the saliva of adult periodontitis patients. General proteolytic and trypsin-like activities were also low in the saliva of localized juvenile periodontitis patients. Furthermore, the reducing agent beta-mercaptoethanol did not activate or inhibit the salivary trypsin-like activity of localized juvenile periodontitis or adult periodontitis patients, although the reductant readily activated partially purified Porphyromonas gingivalis trypsin-like protease in a characteristic manner.(ABSTRACT TRUNCATED AT 250 WORDS)