Peripheral white blood cells (WBC) from normal persons, patients with Guillain-BarréSyndrome (GBS), and persons with a variety of other neurological diseases were maintained in tissue culture. The WBC from patients with GBS demonstrated a greatly increased tendency to become continuous self-proliferating lines of lymphoblastoid cells. Cell lines from both normal subjects and patients were examined by light and electron microscopy. Herpes-like viral particles were found in both varieties of lines. Epstein-Barr virus antigen was demonstrated in most of the cell lines. Animal inoculations of the cells failed to produce any clinical or morphological alterations in the recipients.