Matrix metalloproteinases (MMPs) are zinc-dependent enzymes that degrade the components of the extracellular matrix (ECM) and are known to be the main mediators of human placentation and parturition. Although there are many studies on the roles and distribution of MMPs in human term placenta, so far none of the studies has investigated the distribution of MMP-2, -3 and -9 in different cells of various placental. sites. In this study, we aimed to determine the distribution and enzymatic activities of MMP-2, -3 and -9 with regard to different regions of term human placenta, such as amnion, basal plate, chorionic plate, decidua, chorion laeve, Nitabuch's stria, umbilical. cord and placenta[ villi. Eighteen normal, human term placentas were obtained after vaginal. deliveries. Immunolhistochemistry and zymography were performed for MMP-2, -3 and -9 on placental. tissue sections and protein extracts, respectively. Nearly all tissues showed immunoreactivity for MMPs. The strongest enzymatic activity for MMP-2 was seen in areas where invasive trophoblast cells invaded maternal tissues. MMP-9 had the highest enzymatic activity at the contact region of fetal and maternal. parts, suggesting the importance of MMP-9 in separation of the placenta from the uterine watt during tabor. MMP-3 had a similar localization to MMP-9, suggesting that besides gelatinases like MMP-2 and -9, MMP-3 (stromelysin-1) may also have important roles during tabor. This study describes the site-specific distribution and activities of MMPs and therefore might help in elucidating the molecular mechanisms in pathologies such as premature rupture of membranes. (C) 2007 Elsevier GmbH. Att rights reserved.