Metallothionein(MT) messenger RNA was purified 28-fold from rat liver and was identified by its ability for the protein biosynthesis in cell-free translation systems. Total cytoplasmic RNA was extracted from the Cd injected rat liver by guanidinium thiocyanate method. The total RNA was further fractionated by oligo(dT)-cellulose affinity chromatography. For cell-free biosynthesis of MT-mRNA, rabbit reticulocyte lysate and wheat germ lysate were tested and established the optimal translational conditions for MT-mRNA. The incorporation of [^(35)S]-methionine into MT was a linear function of the amount of poly(A^+) RNA up to 1 ㎍. 4-5 mM Mg^(2+) and 75-85 mM K^+ were found to be the optimal conditions for the MT biosynthesis. Analysis of labelled product was carried out by SDS-PAGE and the gel was analyzed by H₂O₂ gel solubilization and fluorography methods. The activity of MT-mRNA was approximately, 16% and 30%, of the total RNA in the reticulocyte lysate and wheat germ system, respectively.