The killer-cell immunoglobulin-like receptors (KIR) expressed by human natural killer (NK) cells are encoded by a family of genes on chromosome 19. The number of KIR genes varies with haplotype and the individual genes exhibit polymorphism. To investigate KIR diversity we studied KIR cDNA and genes of four human donors: two Caucasians, one Black American and one Asian Indian. From analysis of these donors seventeen novel KIR variants were identified and characterized. Fifteen of the new variants appear to have a simple allelic relationship with a known KIR, whereas two of them combine the sequences of two different KIR genes. Fourteen of the seventeen KIR variants were isolated from the two non-Caucasoid blood donors. These data show that much human KIR diversity remains to be characterized, particularly in non-Caucasoid populations.