We report here on the identification and genomic mapping of a novel member of the family of the ATP-binding cassette (ABC) transporters, ABC7, conserved in mouse and in humans. The ABC7 gene encodes a protein with the typical features of half-transporters, such as those involved in translocation of antigenic peptides or in peroxisomal disorders. ABC7 shows a ubiquitous expression pattern and maps to the X chromosome both in mouse and in humans. The high sequence similarity to those of two yeast half-transporters supports once again the extreme evolutionary conservation of this family of proteins.