The Kell blood group is one of the major antigenic systems in human red blood cells. To determine the location of the Kell gene on human chromosomes, panels containing genomic DNA of human-hamster somatic cell hybrids were hybridized with radiolabeled cDNA probe specific for the Kell locus. Only the samples containing DNA from chromosome 7 gave positive hybridization signals. In situ hybridization analysis, using genomic clones isolated with the cDNA, localized the KEL gene to 7q33. Northern blot analysis of poly(A)+ RNA from human brain, kidney, lung, fetal and adult liver, and bone marrow showed that Kell transcripts were only present in fetal liver and bone marrow. This indicates that the Kell protein, which carries the Kell antigens, may only be expressed in erythroid tissues.