Towards the end of the 19th century intra cervical devices, most of them made of metal, began to be used for contraception. These 'stem' pessaries had a button lodged against the vaginal wall, with a stem protruding into the uterus through the cervix. Intra-uterine devices on the other hand are inserted completely within the uterus. These first appeared early in the 20th century. A very widely used intra-uterine device was the silver Grafenburg ring, developed around 1928. It was still being inserted in patients as late as the 1980s by at least one gynaecologist interviewed by MH. Stem pessaries were still listed in medical catalogues in the 1930s but were probably not used much after this. Intra-uterine devices, however, continued to evolve and in the late 1950s polyethylene was first used. Since then an endless variety of designs in lUDs has been developed, each with its own advantages and disadvantages. The mode of action of intra-uterine devices has still not been established, but it is probable that they prevent pregnancy in several different ways. For large numbers of women they are a satisfactory contraceptive.