Early 2-dose measles vaccination schedules in Africa have been associated with no improvement in coverage due to immunization of the same individuals on both occasions, low return rate, high refusal rate, low vaccine efficacy, and fear of blunting the antibody response. Findings are presented from the study of patterns of vaccination participation, reasons for nonparticipation, vaccination coverage, and the relative efficacy of a 1-dose versus 2-dose schedule in connection with the implementation of an early 2-dose trial in Guinea-Bissau. Children born from September 1994 to January 1996 were randomized into 2 groups receiving either 2 doses of measles vaccine at 6 and 9 months or 1 dose of inactivated polio vaccine (IPV) at age 6 months and measles vaccine at 9 months. 93% of children returned to receive a second dose of vaccine, with the main reason for nonparticipation being the need to travel. About half of the children who did not participate in 1 vaccination took part in the other. There was no sign of low participation or poor return rates in this study of a 2-dose measles immunization schedule at ages 6 and 9 months. The risk of not being vaccinated was lower in the 2-dose group than in the 1-dose group, and the relative efficacy of a 2-dose versus 1-dose schedule was high. These results indicate that with thorough information about the population it may be possible to achieve higher coverage with a 2-dose measles vaccination schedule than with a 1-dose schedule. A 2-dose schedule may be a feasible way of resolving the problems of low coverage and severe measles infection among infants.