Transgenic mice overexpressing transforming growth factor-alpha (TGF-alpha) display an expansion of intrapancreatic fibroblasts and a progressive accumulation of extracellular matrix. This massive fibrosis is associated with an increase in pancreatic size and weight. In parallel, tubular complexes appear that are composed of acinar cells with a decreased height. These acinar cell lose zymogen granules and become transitional cells, which subsequently gain duct cell features. In animals older than one year dysplastic lesions develop, which originate from tubular complexes. Occasionally these dysplastic foci transform to papillary and cystic pancreatic carcinoma. These tumors are positive for the duct-specific antigen Duct-1 and carbonic anhydrase activity indicative of ductal differentiation. Tumors overexpress the epidermal growth factor (EGF)-receptor and p53, but lack K-ras mutations. These data suggest an acinar-ductal-carcinoma sequence in TGF-alpha transgenic mice.