Tektin-t is a part of the tektin protein family, the members of which form filamentous polymers in the walls of ciliary and flagellar microtubules. In mice, tektin-t protein has been localized to the tail of mature sperm, suggesting that it has a role in the formation of sperm flagella and/or sperm motility. In the present study, we have cloned a human orthologue of mouse haploid germ cell-specific tektin-t. The cloned human cDNA and the predicted amino acid sequence showed 82 and 83% identity with mouse tektin-t respectively. Included were a sequence conserved in the tektin B1 family, the TEKTIN2 motif, and the consensus sequence in the tektin protein family composed of nona-peptide. Northern blot analysis of mRNA isolated from various human organs showed that the transcript was approximately 1.7 kb in length and strongly expressed in the testis. Human (h-)tektin-t protein, having a molecular weight of 54 kDa, was exclusively expressed in the testis, whereas two additional stronger bands of 46 and 56 kDa existed in sperm. The h-tektin-t localized specifically to the principal piece of flagella and to the post-acrosomal region. The h-tektin-t gene was assigned to chromosome 1 by a radiation hybrid mapping technique.