Brain tissues from wild forest mice (Clethrionomys) of two similar species were used for isolation and purification of highly homologous polyribosomal poly(A) mRNA sequences by molecular-hybridization with depleted bacterial plasmid DNAs. The isolated highly homologous populations of mRNAs from both organisms were translated in vitro using cell-free protein synthesis systems. Resulting polypeptide chains were analyzed by slab-gel electrophoresis to test the extent of homology between proteins encoded by the homologous mRNAs. Results indicate a lack of correlation between mRNA homology and protein homology.