The putative chaperone Calmegin is required for sperm fertility in mouse and the relevance of the gene to certain cases of human male infertility has been suggested. In the present paper, we have isolated and characterized the human homolog cDNA of the mouse germ cell-specific Calmegin. The entire coding region of the human cDNA showed 80% identity with the previously reported mouse Calmegin. The predicted amino acid sequence showed strong conservation of the two sets of internal repetitive sequences (Ca2+ binding motif), and the hydrophilic COOH terminus, which corresponds to the putative endoplasmic reticulum (ER) retention motif. Our finding will support diagnosis of male infertility. Northern blotting analysis of various human tissues showed that the transcript was 3 kb in length and was expressed exclusively in the testis. Using the fluorescence in situ hybridization (FISH) technique, human Calmegin gene was mapped to chromosome 4q28.3-q31.1.