Pancreatic cells are derived from Pdx1 (pancreatic and duodenal homeobox 1)-expressing progenitors throughout embryogenesis. This conditional transgenic strain expresses Cre/Esr1 from the mouse Pdx1 promoter. Cytoplasmic stores of Cre recombinase translocate to the nuclear compartment upon induction with tamoxifen. When crossed with a strain containing a loxP-flanked sequence of interest, the offspring are useful for generating tamoxifen-induced, Cre-mediated targeted deletions. Immunohistochemistry demonstrates that transgene expression closely follows endogenous Pdx1 patterns. Expression is observed in acini, islet and duct cells but not in mesenchymal cells (endothelial and mesenchyme-derived smooth muscle cells) of the pancreas. Robust cre expression can be detected by E10.5 in pancreatic epithelium. Female mice crossed with Z/AP floxed reporter males (see Stock No.003979) and then injected with tamoxifen demonstrate that the drug is active for less than 48 hours, allowing one to mark progeny of PDX1+ cells indelibly at any stage of development.