Choroideremia (CHM) is an X-linked retinal degenerative disease that results from mutations in Rab Escort Protein-1 (REP1). REP1 acts in the prenylation of Rab GTPases, regulators of intracellular protein trafficking. Rab27a is unique among Rabs in that it is selectively unprenylated in CHM cells, suggesting that the degenerative process in CHM may result from unprenylation and consequent loss-of-function of Rab27a. As a first step towards the analysis of the Rab27a protein in patients, we report here the characterization of the human RAB27A gene. The putative protein encoded by this gene shares 96% identity with the previously cloned rat homologue. The RAB27A gene comprises five coding exons and two non-coding exons, of which one is alternatively used, and spans approximately 65 kb of DNA. There are three alternative poly-A addition sites in the long 3' UTR and also six potential single-nucleotide polymorphisms. The gene is located on chromosome 15q15-21.1, as determined by fluorescent in situ hybridization, and between markers D15S209 and AFM321ZD5 by radiation hybrid mapping.