We have isolated the human homologue of the mouse germ cell-specific transcript Tpx2, which we had previously mapped to mouse chromosome 17. Sequence analysis shows that the human gene is part of the DAZ (Deleted in Azoospermia) family, represents the human homologue of the mouse Dazla and Drosophila boule genes, and is termed DAZLA. Like Dazla and boule, DAZLA is single copy and maps to 3p25. This defines a new region of synteny between mouse chromosome 17 and human chromosome 3. Unlike DAZ, which has multiple DAZ repeats, DAZLA encodes a putative RNA-binding protein with a single RNA-binding motif and a single DAZ repeat. DAZLA is more closely related to Dazla in the mouse than to the Y-linked homologue DAZ (88% identity overall with mouse Dazla compared to 76% identity with the human DAZ protein sequence). Southern blot analysis showed that DAZLA is autosomal in all mammals tested and that DAZ has been recently translocated to the Y chromosome, sometime after the divergence of Old World and New World primates. To investigate the evolutionary relatedness of DAZLA and DAZ further, their partial genomic structures were obtained and compared. This revealed that the genomic organization of both genes in the 5' region is highly conserved. DAZLA is a new member of the DAZ family of genes, which is associated with spermatogenesis and male sterility. Familial cases of male infertility in humans show an autosomal recessive mode of inheritance. It is possible that some of these families may carry mutations in the DAZLA gene.