An intrauterine system (1) for the retention of a biologically active compoun within the uterus of a female mammal is formed by a frame (16) defining an interior space (20) for receipt of a deposit of the compound (22). The frame has an open structure (18) allowing access to a substantial part of an outer surface of the deposit and the deposit has a rate controlling structure that controls a rate of release of the compound within the Uterus. Retention elements (6) are provided on the frame for retaining the frame within the uterus.