The Clinical Studies Section in Boston, Massachusetts is engaged in the identification of persons at high risk of cancer and investigations of causes of their susceptibility. The individuals are found through special referrals from clinicians, self-referral from patients, and clinical observations at Harvard-affiliated hospitals. With informed consent, epidemiologic studies are made to identify the predisposing role of cancer genes and environmental carcinogens. Laboratory studies are performed to clarify biologic mechanisms of susceptibility to cancer. Findings to date show that cancer risk approaches 100% in persons who are carriers of certain cancer genes. Early cancer detection has been achieved in some patients, and appropriate counseling during pre-clinical stages has been provided to other patients. Among high risk patients are those who had one cancer in childhood and are susceptible to develop multiple primary neoplasms. Risk factors in these patients are under study through the computerized Registry of Survivors of Childhood Cancer in Boston. These activities were shown during a 3-month period to an epidemiologist (Dr. Li Jun-yao) from the People's Republic of China as part of a fledgling binational exchange in cancer studies.