A major impediment to our understanding of the biology of stem cells is the inability to distinguish them from their differentiating progeny. We made use of the known association of stem cells with basement membranes to isolate prostate epithelial stem cells. We show that, in vivo, putative stem cells express higher levels of the α₂-integrin subunit than other cells within the basal layer. Approximately 1% of basal cells examined by confocal microscopy were integrin ‘bright’, and these cells can be selected directly from the tissue on the basis of rapid adhesion to type I collagen. This selected population has a basal phenotype, as determined by expression of CK5 and CK14 and lack of expression of the differentiation-specific markers prostate specific antigen (PSA) and prostatic acid phosphatase (PAP), and has a fourfold greater ability to form colonies in vitro than the total basal population. These putative stem cells are distinguished from other basal cells by their ability to generate prostate-like glands in vivo with morphologic and immuno-histochemical evidence of prostate-specific differentiation. These properties are consistent with a stem cell origin. Furthermore, the presence of surface integrins on prostate stem cells suggests that these cells share common pathways with stem cells in other tissues.