Proto-oncogene c-ros codes for a receptor-type protein tyrosine kinase (PTK) sharing high homology with the Drosophila sevenless protein. Recent studies of c-ros expression in mouse by in situ hybridization showed that c-ros was expressed specifically and transiently in the epithelial cells of late embryonic kidney collecting duct and intestine villi. Those investigators suggested that c-ros may play a role in the development of those organelles. In the present study, we have examined the expression profile of c-ros in chicken by RNAase protection and in situ hybridization with riboprobes. Our results showed that in addition to kidney and intestine, low levels of c-ros mRNA could also be detected in lung, testis, thymus and bursa. Expression of c-ros commences during middle to late embryonic stages in those organs and persists into the adult life. In situ hybridization revealed that expression of c-ros was restricted to the epithelial cells of all the tissues examined including kidney, intestine, bursa, thymus and testis. In kidney c-ros was detected in all the epithelial cells of the collecting ducts, in intestine it was detected in the epithelial cells of villi and the underneath crypts. Our finding of c-ros expression in chicken differs from those in mouse in (1) instead of transient expression during the embryonic stage, expression of c-ros in chicken kidney and intestine persists into the adult life and (2) expression of c-ros in renal collecting ducts is not restricted to its growing tips, instead it is expressed in the entire epithelial layer of the ducts. Our results suggest that c-ros may play a role not only in the initial induction events in the organogenesis, but also in the mature function of those organs.