PIP: In order to determine the efficacy of measles vaccine on a remote Pacific atoll, the authors conducted a household-contact study immediately following a large measles epidemic, by examining illness and immunization histories of 258 children ages 1-9 years. Measles vaccine had been administered on Ebeye, Marshall Islands, for 9 years prior to the epidemic and the overall vaccine efficacy rate was found to be 83.5% (95% confidence limits, 74.0-89.1%). Children immunized at 12 or 13 months of age were 1.5 times more likely to get measles than those immunized at 14 months of age (attack rates 9.5% and 6.3%, respectively), but the difference in attack rates was not significant (P=0.63). There was no evidence of any decrease in immunity with the number of years since immunization. Children immunized during 1976 or in August 1977 were found to have a significantly higher measles attack rate (43.1%) than those vaccinated at any other time (6.7%; P 10 -7). This was probably a result of improper storage of measles vaccine during these periods. Since 1970, diphtheria and tetanus toxoids and pertussis (DTP) vaccine and measles vaccine have often been combined in the same syringe in Ebeye clinics and administered together. The measles attack rate for children given DTP and measles vaccines in the same syringe (16.1%) and that for children who were administered the vaccines from different syringes (17.9%) were not significantly different (P=0.84). (author's)