The genetics and physiological role of killer cell immunoglobulin-like receptors (KIR) are briefly reviewed. Haplotype polymorphism of KIR genes resulting in different proportions of genes coding for activatory and inhibitory receptors is emphasized. The participation of KIR molecules in the reactions of natural killer (NK) cells and subpopulations of T lymphocytes is described. Human diseases, in which a contribution of KIR has been found or suspected are listed. Study designs on KIR for realization in Poland are proposed.