The induction of rat liver zinc-thioneins mRNA was studied in a wheat germ cell-free translation system. Liver poly A rich polysomal RNA was isolated from rats which had been injected with zinc sulfate 5 h previously. These RNA preparations stimulated the incorporation of [35S]cystine into trichloroacetic acid insoluble proteins when assayed in the cell-free synthetic system. The translation products were characterized by Sephadex G-75 chromatography in 8 M urea--50 mM beta-mercaptoethanol, by disc gel electrophoresis in 4 M area--Tris-glycine buffer (pH 9.2), and by peptide fingerprinting with pepsin. These results were identical with authentic rat liver zinc-thioneins. The zinc-thioneins mRNA activity in the control rats, however, was minimal. The stimulation in zinc-thioneins synthesis observed in the cell-free synthesis was similar to the increased synthesis of these polypeptides in vivo.