Background & Aims: The surface epithelium of the colon is being replaced constantly with cells derived from the stem cells of the crypt. Although the location of the stem cells is known, there are no markers for these cells. This study tested the hypothesis that colonic stem cells might be isolated and cultured on the basis of specific integrin expression patterns in normal human colonic epithelium. Methods: Integrin expression in normal human colonic mucosa was determined by using indirect immunofluorescence. Crypt cells were then isolated as single cells from normal colon tissues and the expression pattern of integrins was analyzed by flow cytometry. Based on the specific expression of integrin beta1 in colonic crypts, the cells were sorted by using a flow cytometer, and colony assays in soft agar were performed to evaluate the clonogenicity of the sorted cells. Results: By immunofluorescence, the cells located in the lower one third of crypts expressed higher levels of beta1-integrin than the cells in the remainder of the crypt. When isolated crypt cells were stained with the beta1-integrin antibody and examined in a flow cytometer, there were 2 peaks of fluorescence. Sorting of crypt cells based on staining with anti-beta1 integrin antibody produced a cell population with a significantly enhanced ability to form colonies. Conclusions: beta1-integrin is a candidate surface marker for the proliferative zone of the human colonic crypt. Our in vitro culture system for the clonal growth of a single colonic crypt cell suspension could facilitate the identification of other candidate stem cell markers.