A measles epidemic in San Antonio, Texas provided a population of children who were immunized at less than or equal to 10 months of age and reimmunized at greater than or equal to 15 months of age. Of these children, 302 were evaluated for measles antibody by the sensitive enzyme-linked immunosorbent assay (ELISA), and their responses were compared with those of 300 children who had been immunized at the customary time (greater than or equal to 15 months) with a single immunization. There were only five seronegative findings in each group. The children immunized at the customary time did have significantly higher (P less than .001) antibody titers than the children immunized at less than or equal to 10 months and reimmunized at greater than or equal to 15 months. These results indicate that early immunization followed by reimmunization may be indicated when young infants are at significant risk of measles exposure. This approach should not create an increased number of serologically nonresponsive children when reimmunized at greater than or equal to 15 months.