Killer cell immunoglobulin-like receptors (KIRs) are members of a group of molecules that specifically recognize HLA class I ligands and are found on subsets of human lymphopoetic cells. The number of KIR loci can vary between individuals, resulting in a heterogeneous array of possible KIR genes. The range of observed profiles has been explained by the occurrence of two haplotype families termed A and B which can be distinguished on the basis of certain KIR sequences. Here we attempted to determine whether the frequencies of putative KIR loci and the two haplotype groups vary in three ethnically defined, healthy, and unrelated control populations, namely UK Caucasoid (n=136), Palestinian (n=105) and Thai (n=119). We molecularly typed genomic DNA for the presence of 12 putative KIR loci, KIR2DL1, KIR2DL2, KIR2DL3, KIR2DL4, KIR3DL1, KIR3DL2, KIR2DS1, KIR2DS2, KIR2DS3, KIR2DS4, KIR2DS5, and KIR3DS1, using modified PCR sequence-specific primers. The patterns of KIR locus frequencies combined with the similar linkage disequilibrium values suggest that there was a distinction in the distribution of the two broad haplotype groups between the populations studied. The A haplotype was always the most prevalent, but the ratio of A to B varied between populations. The frequency of B haplotype was highest in the Palestinians and lowest in the Thais (Pc<0.0001).