AbstractLymphoblastoid T cell lines from patients with Chediak‐Higashi syndrome (CHS) have been established by stimulating lymphocytes with phytohemagglutinin and interleukin‐2. This culture technique produced T cells containing giant granules which are characteristically seen in peripheral blood leukocytes of children with the disease. The granules were lysosomes as demonstrated by their reactivity with acid phosphatase. Functionally, they exhibited normal natural killer cell activity and/or lectin‐induced cytotoxicity. Variations in function of freshly obtained and long‐term cultured T cells are discussed. These cell lines will permit further studies to elucidate defects in lymphoid cells derived from patients w