Highly purified transferrin mRNA was isolated from rat liver using indirect immunoprecipitation of polysomes with antibodies to rat transferrin and poly(U)-sepharose chromatography. Isolated transferrin mRNA was apparently homogeneous in sedimentation and electrophoretic experiments. Its sedimentation coefficient is 20S and molecular weight 925 000 (chain length 2800 nucleotides). The purified mRNA programmed the synthesis of electrophoretically homogeneous precursor of transferrin. The cell-free translation of transferrin mRNA was highly sensitive to the inhibition by cap analogues (pm7G) that seems being indicative of the capped structure of its 5' end. Hybridization of transferrin mRNA with [3H]poly(U) revealed the discrete length distribution of poly(A) sequences in mRNA (96, 45 and 26 mononucleotides). The proportion of double-stranded (nuclease SI-resistant) regions in transferrin mRNA is as high as 50-60%. Transferrin cDNA was synthesized via the reverse transcription of transferrin mRNA with oligo(dT) primer. This cDNA hydridized with mRNA template and with total polysomal RNA at C0t1/2 values 1.5 X 10(-3) and 3.6 X 10(0) mol nucleotides X 1(-1) Xs, respectively. Hence, the purified mRNA preparation is 2500-fold enriched with transferrin-coding sequences in comparison to the total polysomal RNA from rat liver.