This is the first report on the diethylnitrosamine-induced malignant transformation of human epithelial cells derived from fetal kidney. The transformed cells have prolonged life span and aneuploid karyotypes. They also form anchorage independent colonies in soft agar. With additional one or two NDEA treatments, these cells could elicit poorly differentiated carcinomas in immunosuppressed new-born rats. This experiment indicates that the human fetal kidney cells seem to be a good material for studying the mechanisms of carcinogenesis of human epithelial cell.