Suleimania Children's Hospital, Riyadh, Saudi Arabia was the site of a on-year study, started June 1987, which was designed to investigate measles vaccine failure. The first part of the study consisted of 336 patients with measles. Diagnosis was established on clinical grounds and confirmed by fluorescent IgM analysis. Those patients 9 months and older, which is the legal age of vaccination, comprised 310 subjects. Of these, 29.4% had been vaccinated. This percentage appears to be within the normal range, considering the local coverage rate of vaccination and seroconversion rate, compared with those for other countries. The main cause of vaccine failure was persistent maternal antibodies. The second part from various study involved testing the potency of some samples of measles vaccine obtained from various health centers in the Riyadh region. Potency was found to meet recommended standards.