Activated matrix metalloproteinase-3 (MMP- 3) can contribute to periodontal ligament destruction in adult periodontitis. Since MMP- 3 has been reported to activate proMMP-8 and -9, it was speculated that gingival tissue fibroblast- derived MMP-3 might, in periodontitis, be responsible for activation of gingival crevicular fluid (GCF) neutrophil- derived proMMP-8 and -9. Immunohistochemistry disclosed MMP-3 in gingival fibroblasts in periodontitis. Cultured gingival fibroblasts released only pro-MMP-3 when stimulated with tumor necrosis factor-alpha. However, Western blot revealed partially activated MMP-3, MMP-8, and MMP-9 in periodontitis GCF. Active MMP-8 (p < 0.05) and MMP-9 (p < 0.05) correlated with the presence of active MMP-3. It seems that resident gingival fibroblasts produce pro-MMP-3 in GCF, where it becomes activated, probably by cathepsin G or elastase released by neutrophils. Active MMP-3 then activates neutrophil-derived pro- MMP-8 and -9. Different tissue compartments/cells exert co-operative actions in mutual local MMP activation cascades.