This paper offers a reconsideration of a story preserved both in Josephus and in the Talmud : the opposition between the Pharisian leaders and the Hasmonean dynasty gives rise to a legal creation in the field of « Oral Law » (ancient halakha). This innovation concerns the priests’ filiation and their mother’s position with regard to the laws of purity. The paper tries to replace this story in the historical context of the laws and habits concerning sexuality and men-women relations in Second Temple Judaea of the Hellenistic and Roman age (IIId c. BCE – Ist c. CE).