ABSTRACT
The relationships between gonad dose equivalent rates and incidences of chorionic diseases (i.e., hydatidiform mole, malignant hydatidiform mole, and chorionepithelioma) were analyzed with Kendall's rank correlation and regression methods. Data used were from 11 prefectures of Japan with various dose rates of natural background ionizing radiation between the years 1974 to 1976. The results suggested an association of the incidence of chorionic disease with the radiation dose rate in the very low dose-rate range.