Case ascertainment has been completed in a study of the relationship between residential radon exposure and lung cancer risk in Connecticut and Utah. A total of 945 cases and 945 controls have been interviewed in Connecticut. In Utah, 528 cases and 890 controls have been interviewed and an additional 100 cases have been screened for residence history. Radon measurements are being made in past homes of participants using year-long alpha track etch detectors, in order to estimate cumulative radon exposure since birth or age 25. Detectors have been placed in approximately 70% of the current and past residences of study subjects. Work to verify other past residences and enroll the current occupants in the study is continuing. An analysis file is being created from data collected on the first 100 study subjects at each sit in order to develop strategies for analyzing radon data and for dealing with missing data for homes that cannot be measured. Data collection has been completed in a companion study of childhood cancer risk from residential radon exposure. Data on the 125 cases and 125 controls are being cleaned in preparation for analysis. In a study of childhood leukemia risk associated with residential radon exposure that is being conducted in collaboration with a cooperative childhood cancer treatment group, approximately 200 patients and 300 controls have been found to be eligible and willing to participate. Interviews have been completed and detectors placed for more than 80% of the participants to date. Studies being carried out in Czechoslovakia are assessing the feasibility of studying a variety of health effects potentially associated with radon and other expoures in Uranium mines. Detailed medical and exposure records have been located, access to other sources of health data such as cancer registries, birth records, and vital statistics data has been obtained. Pilot studies have demonstrated the accuracy and completeness of most of these registries, and have demonstrated our ability to link these registries with records of employment in the mines. Basic employment records are being coded and entered into a computerized data base and protocols for full scale studies are being developed.