In this study we investigated the capability of Treponema pallidum to stimulate human dermal fibroblasts to produce interstitial collagenase (MMP-1), which is needed to degrade type I collagen, the most abundant component of the human dermis. When T. pallidum was added to human dermal fibroblast culture, both the amount of secreted MMP-1 and its mRNA levels were increased. Our results show that T. pallidum can stimulate host human fibroblasts to increase the synthesis of MMP-1, which may act as a virulence factor of the organism.