An intrauterinesystem (1) for the retention ofa biologically active compounwithin the uterus of a femalemammal is formed by a frame(16) defining an interior space(20) for receipt of a deposit of thecompound (22). The frame hasan open structure (18) allowingaccess to a substantial part of anouter surface of the deposit andthe deposit has a rate controllingstructure that controls a rate ofrelease of the compound withinthe Uterus. Retention elements(6) are provided on the frame forretaining the frame within theuterus.