Resistance to TGF-beta1 occurred in pancreatic cancer cells suggesting that inactivation of TGF-beta inhibitory signaling pathways may play an important role in human pancreatic cancer. The aim of our study was to determine the presence of alterations in the main putative components of the TGF-beta inhibitory signaling pathways (p15, Smad4, Smad2, TGFbeta-RII, CDC25A). A panel of human carcinomas of the exocrine pancreas orthotopically implanted and perpetuated in nude mice and pancreatic cancer cell lines were studied. p15 gene alterations, mainly homozygous deletions that involved exons 1 and/or 2, were found in the 62.5% (5 of 8) of pancreatic xenografts whereas Smad4 gene aberrations were found in one of eight xenografts and in two of seven cell lines. Additional aberrations in these genes were acquired during in vivo perpetuation and distal dissemination. Paradoxically, TGFbeta-RII overexpression and a decrease in CDC25A protein levels were found in all tumors and cell lines. In one cell line, resistance to TGF-beta1 occurred in the absence of alterations in the genes analysed so far. We conclude that all human pancreatic tumor cells analysed herein have non-functional TGF-beta pathways. The majority of cells harbor alterations in at least one of the putative components of TGF-beta pathways, mainly in p15 and Smad4 genes. These results suggest that inactivation of TGF-beta signaling pathways plays an important role in human pancreatic tumorigenesis.