Analysis of gingival crevicular fluid (GCF) offers a non-invasive means of studying the host response in periodontal disease, and may provide an early indication of the patient at risk for active periodontitis. A number of host markers have been studied for their relationship to disease activity (probing attachment loss or PAL). GCF levels of the acid glycohydrolase beta-glucuronidase (beta G), a marker of primary granule release from polymorphonuclear leukocytes (PMN), have been shown to identify patients with periodontitis at risk for additional PAL. In this multicenter trial, we evaluated (a) the short-term effect of conservative periodontal therapy on beta G activity in GCF, and (b) the relationship of persistently elevated beta G activity to PAL in patients who were monitored for 6 months. The study population included a total of 140 patients with chronic adult periodontitis. 130 patients were on a regular recall schedule, and 10 were previously untreated. After collection of baseline clinical data at all sites, and analysis of beta G in GCF from one site (mesiobuccal) per tooth, the patients received a scaling and prophylaxis. Two weeks later patients were seen for collection of GCF. If elevated enzyme activity was found at 2 weeks, the patients were seen at 3 months for a clinical exam and GCF collection. Clinical parameters were collected from all patients at 6 months. Therapy tended to reduce beta G activity in GCF.(ABSTRACT TRUNCATED AT 250 WORDS)