The human pseudoautosomal region comprises a 2.6 megabase segment of the distal short arms of the X and Y chromosomes. Complete DNA sequence homology between the two sex chromosomes is found in this region, and is believed to be important in mediating X-Y pairing in male meiosis. The only known functional genes in this region are MIC2 and CSF2R; in addition a pseudoautosomal location has been proposed for a genetic locus controlling stature. Here we report the structure of a recently identified pseudoautosomal gene, XE7, and its expression in human tissues. Analysis of genomic and cDNA clones shows that alternative RNA splicing results in the production of two predicted protein isoforms, one containing 385 amino acids and the other with 695 residues. The smaller polypeptide is a truncated version of the larger, and results from the inclusion of a cassette exon that introduces an in-frame stop codon into the mRNA. The XE7 gene appears to be ubiquitously expressed, and the production of both protein isoforms is predicted in each of several tissues examined.