In 1993 questionnaires concerning ethical issues were mailed to 34 committee members of the Monbusho research committee of a large-scale cohort study which started in 1988 including 32 rural communities and 4 occupational groups. The questionnaire survey revealed the following results. 1. In all cohorts, "informed consent" for health questionnaires was carried out, though the methods varied. 2. Although the method varied, informed consent for collection of blood was obtained in 28 (77.8%) of the 34 cohorts. The committee decided that the collected specimens without consent is not used for study. 3. The protection of privacy was deliberately planned and has been carefully carried out in the cohort study. 4. The committee members' concerns for ethical issues has increased after joining the cohort study. 5. The attitudes of informed consent for collection of blood at mass screenings showed wide differences among research objects and researchers. These results suggested that the research members had a considerably high concern for ethical issues and that ethical considerations in epidemiological studies should be continued in Japan.