Hepatocytes of rats stimulated by turpentine into a hyperfibrinogenemic state produce sufficient quantities of fibrinogen to permit unequivocal identification of specific polysomal complexes involved in the synthesis of this molecule. Monospecific antibodies directed against intact fibrinogen and one of its subunits, the gamma-chain, have shown two size classes of polysomes. Furthermore, it seems possible that polypeptide chain assembly may occur by having completed nascent chains bind to partially completed chains that are still attached to the polysome.