The sequence of a new HLA-Cw*04 allele has been identified in a Laotian family. This allele, designated Cw*0406, differs from Cw*0403 by a single nucleotide substitution at codon 156 (CGG-->CTG) in the alpha2 domain, leading to an amino acid change from Arginine to Leucine. Further screening by specific amplification of two ethnically different populations, i.e. French (n=150) and Lebanese (n=100), provided no case of Cw*406, suggesting that the distribution of this allele may be restricted.