In a 19 month old girl and a 10 month old girl the Guillain-Barre Syndrome developed within a week after they received, respectively, live measles-rubella vaccine and live measles vaccine. The older child was immune to the rubella at the time of vaccination, but both girls demonstrated a primary measles antibody response. Serum obtained during the acute and convalescent stages from the younger child was tested for antibodies against the herpes viruses (herpes simplex, Epstein-Barr virus, cytomegalovirus and varicella-zoster) and found to be negative.