Using cDNA microarray hybridization from a human testicular cDNA library, one gene exhibiting threefold difference at expression level between adult and embryo human testes was named nDnaJA1 (a new alternative isoform of human DnaJA1 which was also named HDJ2/Hsdj/dj2, a human HSP40 homologue), which was believed to be involved in testis development and spermatogenesis. Multiple tissue polymerase chain reaction (PCR) results showed that nDnaJA1 expressed highly in testis and lung but low in thymus, prostate, colon and liver. The results of the other members of DnaJA1 family (GenBank accession numbers: D13388 and BC008182) showed that they were widely expressed. D13388 and BC008182 were highly expressed in sperm while nDnaJA1 was faintly expressed by reverse transcriptase PCR. Protein motif analysis of nDnaJA1 sequence revealed motifs of DnaJ. nDnaJA1 was considered as type I DnaJ like the other members of DnaJA1 family.