To elucidate the role of LKB1 in proglucagon-expressing enteroendocrine cells, and the possible contribution of these cells or their progenitors in the formation of polyps in PJS, we have crossed mice bearing floxed Lkb1 alleles with mice bearing a proglucagon-specific Cre recombinase. The gene discussed is STK11; the disease is Peutz-Jeghers syndrome.