Abstract A compulsory immunization policy against measles was introduced in the Socialist People's Libyan Arab Jamahiriya in 1972. Data are presented to show that a decreased incidence of measles followed this programme. Nevertheless, measles epidemics still occur and the serological status of the population has, therefore, been examined. In the area of Tripoli, measles haemagglutination-inhibiting (HI) antibodies were found at a titre of ⩾ 1:10 in 97% of the adult population, and in 78%, 100% and 97·1% of schoolchildren of primary, preparatory and secondary schools respectively. The relatively high HI titres observed, particularly in adults, imply that antigenic restimulation of antibody against measles occurs and thus that coverage by immunization remains inadequate. Increased efforts to improve immunization coverage at an early age are recommended.