PIP: The study separately tested the release rate of a contraceptive vaginal ring (CRV) on 35 and 51 days in vitro by using two sets of CRV. The CRV was bathed in the medium in the reagent bottles kept in a horizontally vibrated thermostat bath at 37 centigrade. Megestrol acetate was assayed by measuring the ultraviolet absorption of the solution at 290nm. The results showed that the release rate was high in the first seven days and declined to constant level. The two average release rates were 283 mcg and 288 mcg day, respectively. It indicated repeatable release rate was as expected. The curve in the regression equation showed CRV was zero released medicine. In addition, comparing CRV vibrated horizontally and vertically, there was no significant difference between two vibrating ways. This method proved to be useful for the measurement of the release rate of CRV containing megestrol acetate. (This work was supported by WHO-HRP).