We have Isolated a population of vesicular carriers involved in the transport (transcytosis) of proteins from the basolateral to the apical plasma membrane of hepatocytes. The obtained fraction was enriched in compartments containing known transcytosed proteins and depleted in elements of the secretory pathway, Golgi elements, basolateral plasma membrane, as well as early endosomal components. The fraction was analyzed by biochemical and Immunological procedures. Antibodies raised against the proteins in the fraction recognized a single 108K antigen. Based on its subcellular distribution, the 108K antigen may represent a novel marker for transcytotic vesicular carriers. © 1991.