Summary Early clinical trials indicate that it is possible to immunize children with live attenuated measles virus. The susceptible subjects develop either no symptoms at all or a modified measles with fever, leukopenia, and a faint eruption. Koplik spots are uncommon. These children have no catarrhal symptoms and do not appear toxic. All of the susceptible children developed a significant titer of neutralizing antibodies. No complications occurred in any of our cases. The urgent need of a measles vaccine is stressed, and there are indications that measles immunization as a routine procedure may not be too distant.