Chediak-Higashi syndrome (CHS) is a rare, autosomal recessive, multisystem disorder in which severe immune deficits are accompanied by abnormalities of pigmentation, blood clotting, and neurologic function. There is no specific treatment, and without bone marrow transplantation, most patients succumb to frequent bacterial infections or to a lymphoproliferative syndrome that appears to result principally from lack of natural killer cell function. Disorders similar to human CHS occur in many mammalian species, the most important being the beige mouse, long considered a likely homologue of human CHS. This supposition has recently been confirmed by the mapping, cloning, and mutation analysis of the homologous human CHS1 and mouse beige genes. Identification of the human CHS1 gene, and the availability of a ready mouse model for human CHS, will likely facilitate investigation of the disease pathophysiology and the development of novel and specific treatments for the disorder.