SNAP-23 plays an important role in the regulation of vesicle trafficking in mammalian cells. In this report, we have determined the exon/intron organization of the mouse SNAP-23 gene. The SNAP-23 gene spans 31kb of the mouse genome and consists of eight exons interrupted by seven introns. The exon organization of the mouse SNAP-23 gene is identical to that of the related SNAP-25 gene in both chicken and Drosophila, suggesting that SNAP-23 arose by duplication of the SNAP-25 gene. Primer extension analysis revealed a major transcription start site approximately 112bp upstream of the translation start site. Like many ubiquitously expressed housekeeping genes, the proximal promoter region for the mouse SNAP-23 gene lacks consensus TATA and CAAT boxes. The SNAP-23 gene was localized to mouse chromosome 2 at band 2E5 using both fluorescence in-situ hybridization and radiation hybrid panel mapping studies. The identification of the structure of the mouse SNAP-23 gene reveals that the overall exon organization of SNAP-25 family members is conserved throughout evolution.