A cell line (RIE-1) of epithelioid morphology was established from rat small intestine. RIE-1 cells possess the normal rat diploid number of chromosomes (42) up to at least passage 20. Both early (less than 10) and late (greater than 20) passage cells are non-tumourigenic and do not form colonies in soft agarose. RIE-1 cells bind two epithelial-specific monoclonal antibodies. In addition, the cells exhibit a network of cytoskeletal filaments which are labelled by an antiserum to keratin. These findings provide strong evidence for an epithelial origin of the RIE-1 cell line.