Matrix metalloproteinases (MMPs) are responsible for remodeling and degrading extracellular matrix and basement membrane components. MMP-3 and -8 levels were assessed in this study during the early healing phase following a guided tissue regeneration (GTR) procedure. 32 patients, having 2 or 3 walled intrabony defects of PD > or =6 mm, were stratified into 2 groups on the basis of age, sex, smoking status and disease severity. All intrabony defects were treated using the resorbable Guidor membrane but only 1 group of patients was given a pre-operative dosage of antibiotic (3 g amoxycillin). GCF samples for the quantification of MMP-3 and -8 levels were obtained from the intrabony site where a membrane was placed (membrane site), from the non-adjacent site on the adjacent tooth which was involved in the surgical flap (surgical control site), and from a healthy site (healthy) on the contralateral side. The GCF samples taken at baseline, 1 week, 4 weeks and 3 months after surgery were analyzed using an enzyme linked immunoabsorbent essay (ELISA) for MMP-3 and using a time-resolved immunofluorescence assay (IFMA) for MMP-8. MMP-3 was detected in a very low % of sites at baseline while relatively high levels of MMP-8 were detected at all 3 types of sites at baseline. MMP-8 levels increased for all sites at week 1, and this was statistically significant for the membrane site, but at week 4, the levels decreased for both the membrane and the surgical sites. There was no statistically significant difference between the levels of MMP-3 and -8 in the antibiotic and non-antibiotic group. Collagen remodelling occurs during the early wound healing period following surgical and regenerative procedures. The levels of MMP-3 and -8 in GCF appear to reflect these processes. Interestingly, the presence of the membranes appeared to increase the levels of MMP-3 and -8 and may relate to the resorption of the resorbable membrane by host systems.