Mesenchymal stem cells (MSCs) have been cultured from many sources, including bone marrow and liver. To further support our hypothesis that MSCs exist in most postnatal tissues, we isolated a clonogenic, multipotent, rapidly proliferating population of cells from a fetal pancreas and termed them "pancreas-derived mesenchymal stem cells" (PMSCs). They withstood being passaged as many as 30 times without sustaining significant structural changes. In this study, we showed that PMSCs are positive for CD44, CD29, and CDI3 but negative for CD34 and HLA-DR and that they stained with collagen I and III but not with von Willebrand factor antibody. During the log phase of growth, PMSCs proliferated, doubling in population in about 30 hours. Cell-cycle analysis showed that more than 90% of cells were in the G0 and G1 phases, whereas a small subpopulation of cells were actively engaged in proliferation (S＋G2＋M＝3.55%). Under differentiation culture conditions, PMSCs differentiated into cells of osteogenic, chondrogenic, and adipogenic lineages. These results demonstrate that PMSCs can be isolated from human fetal pancreas by means of their adherent ability and that they are capable of self-renewal, propagation, and multipotent differentiation. (J Lab Clin Med 2003; 141: 342-9)