Adult human stem cells are employed in novel treatments and bio-artificial devices. Recent studies have identified an abundant source of stem cells termed adipose-derived adult stem (ADAS)-cells in the subcutaneous adipose tissue. Under appropriate culture conditions ADAS-cells differentiate to various cell types, including chondrocytes, adipocytes, and smooth muscle cells. Aiming at epithelial differentiation this study investigated the effect of all-trans retinoic acid (ATRA) on human ADAS-cells. ATRA-induced cytokeratin 18 expression in ADAS-cells and nearly abolished vimentin expression as shown by Western blot. In immunofluorescence, the formation of keratin fibers in ATRA-treated ADAS-cells could be observed. The percentage of ADAS-cells being able to undergo epithelial differentiation as quantified by FACS-analysis was above 80%. Inhibition of cell growth by ATRA was shown using DAPI- and MTT-assays. ATRA can differentiate ADAS-cells toward the epithelial lineage. This finding, along with a previously described neural differentiation, shows that ADAS-cells have epithelial potential. (c) 2005 Elsevier Inc. All rights reserved.