Relationship of Genetic Differences to the Development of Chromosome Abnormalities

* INCLUSION CRITERIA - EXPOSED POPULATION: Individuals eligible to be included in the 'exposed' population include all those employed from 1948-1972 in the three plants directly related to nuclear-weapon production (nuclear reactor, radiochemical production plant, plutonium production plant), who have remained local residents, and who have estimates of their external gamma dose and internal plutonium exposure. Some eligible workers did not have any plutonium exposure, but are still eligible to be included in the exposed sample due to their external radiation exposure. All participants are required to be cancer-free at the time of enrollment. EXCLUSION CRITERIA - EXPOSED POPULATION: Individuals who have a medical history of radiation therapy or a blood transfusion within the previous year will be excluded. As the sample size would not be adequate to examine their risk separately, Tartars and Bashkirs will not be included in the study. INCLUSION CRITERIA - COMPARISON GROUP: The comparison population will be drawn from current and former workers in the auxiliary plants (water treatment facility and mechanical repair plant) at the Mayak facility. Included will be a stratified random sample of these workers who were employed from 1948-1972, who have remained local residents, and who have estimates of their external gamma dose. Individuals selected will be frequency-matched according to age (5 year age groups) and gender to the exposed worker population.