Allelic polymorphism of killer immunoglobulin-like receptor (KIR) genes may affect receptor expression as well as function. We used a combination of allele group-specific primers and DNA sequencing techniques to verify our KIR genotyping primers in polymerase chain reaction and identified three KIR3DL1 alleles. By sequencing some introns of 3DL1 in 18 genomic DNA samples, we found that a 4-bp insert in intron 1 of 3DL1*002 exists in multiple alleles, but that a 2-bp deletion in intron 7 is unique to 3DL1*01501 and that a 19-bp insert in intron 1 seems specific to the CEPH family 1416. Our data suggest that extensive KIR gene polymorphisms are ubiquitous as well as quite complex.