We undertook a study to demonstrate the potential contribution of oral-fluid (OF) antibody prevalence surveys in evaluating measles vaccine campaigns. In Asela town, southern Ethiopia, oral fluids were collected from 1928 children aged 9 months to 5 years attending for campaign immunization in December 1999 and 6 months later, from 745 individuals aged 9 months to 19 years, in the same location. Measles antibody status was determined by microimmune measles specific IgG enzyme immunoassay (EIA). Antibody prevalence was estimated at 48% in children attending for vaccination (pre-campaign), and 85% post-campaign in the comparable age group. The estimated reduction in the susceptible proportion was 75%. In older children the proportion antibody negative post-campaign was 28% in 7–9 year olds, and 13% in 10–14 year olds levels of susceptibility which raise concern over continued measles transmission. This is the first evaluation of a measles vaccine campaign based on oral-fluid seroprevalence surveys and it demonstrates the merit of oral-fluid surveys in informing health authorities about vaccination strategy refinement.