There are very few reports on smallpox vaccination in newborn infants, since it is not the rule to give smallpox vaccination in the neonatal period. This report is to present a clinical observation of smallpox vaccination in newborn infants during the experiment of simultaneous vaccination with BCG and smallpox vaccines. BCG vaccination has been done to the newborn infants for many years in this country, but it has been only limited to a number of newborn babies who were born at hospitals. A large campaign of BCG vaccination has been undertaken on school children, but again only a small part of the preschool children and infants has been vaccinated with BCG. Because tuberculous meningitis is still an important cause of death of young children in Taiwan, and statistical survey shows there has been no decrease of cases of tuberculous meningitis, but the deaths due to other types of tuberculosis have markedly diminished since when the island-wide BCG program was started in 1951, therefore a 1arg scale of BCG vaccination to those before the school age is necessary for the prevention of occurrence of tuberculous meningitis. For such a large scale campaign of BCG vaccination it may be very convenient if BCG vaccination can be done at the same time when the children receive smallpox vaccination, because mothers are already well aware of the importance of smallpox vaccination but not that of BCG vaccination. For this reason the Provincia1 Taipei Tuberculosis Control Center has been planning to recommend the health centers to give BCG vaccination simultaneously with smallpox vaccination^2,3 Therefore a preliminary experiment of simultaneous vaccination with BCG and smallpox vaccines has been done on newborn infants, since it is easier to make a control study on newborn babies and BCG vaccination on newborn babies has been practised for many years at the National Taiwan University Hospital. This report presents only a clinical observation of smallpox vaccination in the newborn babies during this experiment.