Pseudoautosomal boundary-like (PABL) elements have been found at transition sites between genomic regions with different GC-contents. A new PAB related sequence was found immediately adjacent to the S71 provirus on human chromosome 18q21.1-2 (officially designated the SSAV1 locus). The S71 PABL element was full-length as defined by comparison with elements identified at the pseudoautosomal boundaries of the sex chromosomes and in the MHC region. The 3'-ends of all PABL elements showed significant homology to functional CpG-islands, indicating that this similarity is a new common feature of PABL elements.