The McLeod syndrome is a rare X-linked recessive disorder characterized by blood group, neuromuscular and haematopoietic abnormalities. It is caused by XK gene defects and may include large deletions in the Xp21 region. Analysis of three unrelated McLeod patients for the presence of the XK, DMD, CYBB, ETX1, RPGR and OTC loci, as well as for the DXS709 marker, revealed deletions from the 39th exon of DMD to the ETX1 locus (patient Be), from the XK to RPGR loci (patient Bi) and from the XK to CYBB loci (patient Lh). All three patients normally expressed the Lutheran (Lu) red cell antigens, thus excluding the interval between the RPGR and DMD genes as site of the XS locus, previously mapped to the Xp21.2-Xq21.1 region and thought to regulate the expression of the LU blood group gene on chromosome 19.