We here isolated and characterized a cDNA clone encoding 40-kDa heat-shock protein hsp40 from cDNA expression library of human placenta by immunoscreening with anti-hsp40 antibody. N-terminal amino acid sequence (48 residues) deduced from the base sequence was completely identical to that of hsp40 purified from HeLa cells. Deduced amino acid sequence of the cDNA is homologous to bacterial DnaJ heat-shock protein and its homologues in yeast such as SCJ1, YDJ1(MAS5), SIS1, SEC63 and Zuotin. Nucleotide sequence identity between hsp40 and HDJ1 (another human DnaJ homologue) is more than 98%, suggesting that these two proteins are the same gene product.