Anti-JAHK, an antibody directed toward a low-incidence antigen in the Rh system, was detected during routine antibody identification in a male donor who had no history of transfusion. Examples of anti-JAHK have been found in sera containing multiple antibodies to low-incidence antigens. The first report of anti-JAHK was in 1995 and described the association of the JAHK antigen with the rG haplotype. Our results confirm this association.