Abstract 281 newborn babies whose mothers had chickenpox and 25 whose mothers had herpes zoster during the perinatal period were investigated. IgG antibody was present at birth in all babies born more than 7 days after the onset of maternal chickenpox. When the mother's rash appeared 7-3 days before delivery progressively fewer babies were born with antibody, and no infant born less then 3 days after the onset had antibody at birth. Infants were given 100 or 250 mg of anti-varicella-zoster immunoglobulin (VZIG) shortly after birth or the onset of post-natal maternal chickenpox. 1 infant died, without neonatal varicella. Of the 280 surviving infants 169 (60%) were infected—134 (48%) with chickenpox and 35 (13%) without clinical features. The clinical attack rate was highest (60%) in infants whose mothers had chickenpox between 7 days before and 7 days after delivery. Chickenpox was severe in 19 infants, 16 of whom were exposed to maternal chickenpox between 4 days before and 2 days after delivery. There was no evidence that a severe outcome was associated with transplacentally acquired infection. Perinatal maternal herpes zoster did not cause neonatal infection. VZIG should be given to infants at risk, including those whose mothers have chickenpox during the last 7 days of pregnancy.