The incidence of measles in England and Wales has fallen since the national vaccination campaign in November 1994, in which 92% of children aged 5 to 16 years were vaccinated. A total of 148 confirmed cases with onsets in the 18 months from January 1995 to June 1996 have been ascertained. Notified cases did not provide a reliable measure of incidence: 11,343 suspected cases were notified in the same period, 6426 (57%) of whom were tested for salivary antibody. Only 90 (1.4%) of cases tested were confirmed. Many confirmed cases occurred in small clusters; 12 imported cases were identified. The pattern of small, local clusters is what would be expected from the introduction of imported cases into a population with herd immunity. Serological surveillance showed that the campaign produced a significant fall in the proportion of 5 to 16 year old children with low levels of measles antibody: the proportion with levels < 50 mIU/ml fell from 8.4% to 2.1%; the proportion with levels < 100 mIU/ml fell from 15.7% to 6.6%. About 15% of 2 to 4 year old children had antibody levels < 100 mIU/ml before and after the campaign. The addition of a routine second dose of measles vaccine (as measles, mumps, and rubella vaccine) to the vaccination schedule will provide another opportunity to immunise these children before they start school. The two dose vaccination programme should maintain the herd immunity of the population and the elimination of endemic measles transmission.