The reactogenicity and antigenic activity of live measles vaccine prepared from strain Leningrad-16 were assessed for 4 territories, two of which were exposed to radiation contamination as a result of the Chernobyl accident. The study was carried out at the L. A. Tarasevich State Institute for Standardization and Control of Viral Preparations. The vaccine was weakly reactogenic in all the regions; no grave or uncommon reactions to its administration were observed. Serologic studies revealed a high antigenic activity of the vaccine. The level of seroconversion was estimated as 98.5%. The study failed to detect any appreciable effect of radiation contamination on the tolerance to vaccine or level of immune response.