We constructed cDNA libraries from 8-9-S poly(A)-rich RNA from regenerating rat liver, isolated clones specific for ribosomal protein L27 and determined the nucleotide sequences of the cDNA clones. The longest cDNA consists of 15 base pairs from the 5' leading sequence, the entire coding sequence of 411 base pairs, and the 3' trailing sequence of 59 base pairs including the poly(A) tail. The primary structure of protein L27 was deduced from the sequence of nucleotides. Protein L27 contains 135 amino acids and has a molecular mass of 15,666 Da. The amino-terminal sequence agreed well with the published partial amino acid sequence and the calculated amino acid composition is also consistent with the reported composition determined for the hydrolyzate of L27.