Genomic DNA from a panel of 41 healthy unrelated Japanese individuals was typed for the presence or absence of 16 KIR genes and pseudogenes. Only eight different KIR genotypes were found. Group A haplotypes outnumbered group B haplotypes in frequency by approximately 3:1, with individuals having two group A haplotypes accounting for 56% of the panel. The frequency of A haplotypes in the Japanese is higher than that observed in other populations. Flow cytometric comparison of KIR expression in 19 panel members showed considerable diversity in NK cell repertoire, which was also seen within the group of individuals having two A haplotypes. This diversity is likely due to allelic polymorphism in expressed genes of the A haplotype. In comparison to other populations, the Japanese appear less heterogeneous in KIR genotype as assessed by gene content.