A number of cDNA clones in summary encoding 700 amino acid residues from the N-end of rat liver elongation factor 2 (EF-2) and including 49 nucleotides of the 5'-untranslated mRNA region have been obtained. EF-2 cDNA clones were isolated from gradually constructed small (1000-5000 clones) specific cDNA libraries using the primer extension method for synthesis of the first cDNA chain. The complete primary structure of cDNA and protein EF-2 from rat liver was derived taking into account the primary structure of the 3'-terminal region EF-2 cDNA previously reported [(1986) Proc. Natl. Acad. Sci. USA 83, 4978-4982]. Comparison of this cDNA with hamster cDNA has shown that (i) the base sequences had a 89.7% homology while that of the 5'-untranslated region was 73%; (ii) there are two amino acid replacement in rat liver EF-2 as compared with hamster EF-2.