Changes in the pattern of isoperoxidases and the specific activity of peroxidases were examined from cotyledone, hypocotyl and root portion of the Korean radish seedlings grown for 3, 5 and 7 days. The specific activity of peroxidases was very high in the root compared with that of hypocotyl and cotyledone portion of the seedlings and peroxidase isozyme patterns in these three organs were changed during entire growth periods. Total cellular RNA was isolated from hypocotyl and root portion of the seedlings with guanidium thiocyanate and guanidine HCl method. The total RNA was further fractionated by oligo (dT)-cellulose chromatography. For translation of peroxidase mRNAs in cell-free protein synthesizing system, rabbit reticulocyte lysate was tested and the optimum translational conditions of peroxidase mRANs were determined. The poly(A) +RNA and poly(A)-RNA isolated from hypocytyl and root portion of the seedlings grown for 5 and 7 days were translated in vitro and the correlation between the changes in the expression pattern of isoperoxidases and qualitative and quantitative changes in peroxidase mRNA populations was investigated. The peroxidase activity of poly(A)-RNAs was much higher than that of poly(A)+RNA in seedlings grown for 7 days when compared with that of poly(A)-RNAs from seedlings grown for 5 days.