A convenient method for the partial purification of functional, poly(A)-rich mRNA is described. The method involves annealing poly(A)-rich mRNA to oligothymidylic acid-cellulose columns and eluting it with low ionic strength buffers. Rabbit globin mRNA was purified using this technique and tested for its ability to direct rabbit globin synthesis in an ascites tumor cell-free system. Since various mammalian mRNAs are poly(A)-rich and can be translated in the ascites cell-free system, this method is useful for isolating specific mRNAs. The expression of genetic information in higher organisms depends on detecting and isolating gene-specific mRNA. Unlike bacterial systems, isolating mRNA in animal cells has relied on radioactive labeling and molecular weight differences. However, methods exploiting other mRNA properties are also valuable. Putative mRNAs from animal cells differ from other RNA species by containing long poly(A) regions. These regions may be involved in mRNA transport from the nucleus to the cytoplasm. Several methods have been used to detect poly(A) regions or putative mRNAs, including oligo(dT)-cellulose, poly(U)-cellulose, and nitrocellulose filters. Rabbit globin mRNA contains poly(A) regions, making it suitable for preparative purification. In this study, oligo(dT)-cellulose chromatography was used to separate globin mRNA from ribosomal RNA in crude polysomal extracts. This method is effective due to the sensitivity of in vitro rabbit globin synthesis assays. The purified globin mRNA was tested for its ability to direct protein synthesis in the cell-free system, showing high activity. The purified mRNA was analyzed using SDS-PAGE and tryptic peptide analysis, revealing a 17,000 dalton polypeptide co-migrating with rabbit globin. Tryptic digestion and cation exchange chromatography confirmed the mRNA's ability to direct synthesis of rabbit globin. Sucrose gradient centrifugation resolved the mRNA into distinct peaks, with the 9S fraction showing the highest activity. The method is useful for isolating mammalian mRNAs, as many contain poly(A) regions. The procedure is efficient, repeatable, and suitable for further purification. The study also highlights the potential of the ascites tumor cell-free system for testing tRNA suppressors of mammalian termination codons.A convenient method for the partial purification of functional, poly(A)-rich mRNA is described. The method involves annealing poly(A)-rich mRNA to oligothymidylic acid-cellulose columns and eluting it with low ionic strength buffers. Rabbit globin mRNA was purified using this technique and tested for its ability to direct rabbit globin synthesis in an ascites tumor cell-free system. Since various mammalian mRNAs are poly(A)-rich and can be translated in the ascites cell-free system, this method is useful for isolating specific mRNAs. The expression of genetic information in higher organisms depends on detecting and isolating gene-specific mRNA. Unlike bacterial systems, isolating mRNA in animal cells has relied on radioactive labeling and molecular weight differences. However, methods exploiting other mRNA properties are also valuable. Putative mRNAs from animal cells differ from other RNA species by containing long poly(A) regions. These regions may be involved in mRNA transport from the nucleus to the cytoplasm. Several methods have been used to detect poly(A) regions or putative mRNAs, including oligo(dT)-cellulose, poly(U)-cellulose, and nitrocellulose filters. Rabbit globin mRNA contains poly(A) regions, making it suitable for preparative purification. In this study, oligo(dT)-cellulose chromatography was used to separate globin mRNA from ribosomal RNA in crude polysomal extracts. This method is effective due to the sensitivity of in vitro rabbit globin synthesis assays. The purified globin mRNA was tested for its ability to direct protein synthesis in the cell-free system, showing high activity. The purified mRNA was analyzed using SDS-PAGE and tryptic peptide analysis, revealing a 17,000 dalton polypeptide co-migrating with rabbit globin. Tryptic digestion and cation exchange chromatography confirmed the mRNA's ability to direct synthesis of rabbit globin. Sucrose gradient centrifugation resolved the mRNA into distinct peaks, with the 9S fraction showing the highest activity. The method is useful for isolating mammalian mRNAs, as many contain poly(A) regions. The procedure is efficient, repeatable, and suitable for further purification. The study also highlights the potential of the ascites tumor cell-free system for testing tRNA suppressors of mammalian termination codons.