A 1-year-old white girl with typical signs and symptoms of Chédiak-Higashi syndrome showed impaired delayed hypersensitivity. The patient had frequent upper respiratory tract infections in the past, including an attack of viral pneumonia. Transfer factor prepared from 2 × 108 normal lymphocytes was given intramuscularly. Following this, the patient developed delayed hypersensitivity responses. Passive transfer of histoplasmin reactivity from the donor to the recipient was also accomplished. The patient exhibited evidence of improved immunity.