Pancreatic gene expression was analyzed in the rat during taurocholate-induced pancreatitis, with emphasis on the postacute phase where regeneration occurs. Increased expression of cellular oncogenes c-myc and H-ras followed a pattern typical of tissular regeneration. The c-myc protein was immunolocalized to acinar cells, in which amylase expression was concomitantly decreased. Such modifications in the program of gene expression and the presence of numerous mitotic figures confirmed participation of acinar cells in regeneration. There was, on the contrary, no evidence of duct cell proliferation and pancreatitis did not influence the expression of two mRNAs encoding ductal proteins. Expression of villin, which is a marker of the embryonic pancreas, increased by five times during pancreatic regeneration. The protein was localized to the tubular complexes, suggesting that cells forming those structures had returned to a protodifferentiated stage in which they should have recovered pluripotency. They might therefore supply the pancreas with any cell type needed to reconstitute functional parenchyma.