TGF-β strongly promotes local tumor progression in advanced epithelial tumors, though the underlying mechanisms are poorly understood. In the present study, we demonstrate the potential of TGF-β to increase the invasiveness of the pancreatic cancer cell lines PANC-1 and IMIM-PC1. TGF-β–induced tumor cell invasion occurred in a time-dependent manner, started after 12 hr and continued to increase even 48 hr after a single application of the growth factor. Blocking of secreted TGF-β1 by application of neutralizing antibodies 24 hr after TGF-β treatment completely prevented the sustained effects of TGF-β on tumor cell invasion. Together with our previous observation that TGF-β1 up-regulates its own expression in both cell lines, our data suggest that TGF-β1 acts in an autocrine manner to maintain tumor cell invasion. As measured by Northern blot hybridization and zymography, TGF-β treatment of PANC-1 and IMIM-PC1 cells resulted in strong up-regulation of expression and activity of both matrix metalloproteinase-2 (MMP-2) and the urokinase plasminogen activator (uPA) system. Treatment with MMP inhibitors or inhibitors of the uPA system caused significant reduction of TGF-β–induced invasiveness in both cell lines. In contrast, expression and activity of MMP-2 and uPA as well as tumor cell invasiveness remained unaffected in cell lines with defects of the TGF-β type II receptor (MiaPaca2) or the Smad4 gene (IMIM-PC2 and CAPAN-1). In these cell lines, TGF-β also failed to auto-induce its own expression. In conclusion, our results suggest that TGF-β1 is a strong promotor of pancreatic cancer progression. TGF-β thereby acts in an autocrine manner to induce tumor cell invasion, which is mediated by MMP-2 and the uPA system. © 2001 Wiley-Liss, Inc.