Killer immunoglobulinlike receptors (KIRs) are expressed on natural killer and T cells. Both inhibitory and noninhibitory forms have been described, leading to inhibition or continuation of cellular killing activity. The natural ligands identified so far of KIRs are class I human leukocyte antigens (HLA). In particular, the interaction of some KIRs with HLA-Cw has been well characterized. Recent work has implicated KIRs in affecting the outcome of hematopoietic stem-cell transplant (HSCT). This may well lead to a requirement for prospective KIR typing of donor and recipient. We have utilized different typing systems (two using polymerase chain reaction-sequence-specific primers, and one using polymerase chain reaction-sequence-specific oligonucleotide probes) in three separate laboratories to characterize the KIR gene complement of 25 cell lines from the 10th International Histocompatibility Workshop. There were consistent results in 22, and minor differences in 3. When compared with previous results for some of these cell lines, no further differences were found. The differences are due to typing of KIRs KIR2DL1 and KIR2DS5, and may be explained by technical differences or the inability to type new variants. Further improvements in typing may be required if population and clinical studies are to produce accurate results.