Our results with NK cells, together with data showing that delivery and processing of proteins in the lytic granules in cytotoxic T cells (CTLs), lysosomal degradation of endogenous proteins in fibroblasts, and acidification of enlarged lysosomes in B cells and fibroblasts are unaffected in patients with CHS,24, 65, 66 indicate that the large granules in LYST-deficient cells are functional. The gene discussed is LYST; the disease is Chediak-Higashi syndrome.