Two patients developed Guillain-Barré syndrome after varicella-zoster infection; a 4-year-old boy after chickenpox and a 74-year-old man after shingles. Both had decreased CD8-positive lymphocytes in the blood during the course of their illness. These cases and others reported in the literature suggest that varicella-zoster infection is a significant but rare trigger factor of Guillain-Barré syndrome. An alteration in the balance of helper and suppressor lymphocytes may be an important pathogenetic mechanism.