the aim of the present study was to evaluate the effect of a progesterone releasing intravaginal device plus the injection of pgf2α at removal and the application of hcg on day 5 after withdrawal on the ovarian activity in cyclic mares. additionally, pregnancy rates were evaluated at the end of the study. animals were divided into two groups: treated with an intravaginal device containing 1.38 g progesterone during 8 days plus pgf2α at the removal time and an hcg injection to animals with a follicle with a diameter ≥ 30 mm on day 5 and controls (no treatment). four days after removal, animals were mated. plasma progesterone concentrations remained 2.1 ng ml-1 during the period that the devices were kept into the vagina. an ovulatory follicle between the device removal and hcg application was observed in 83.4% (25/30) of the treated animals: 68% (17/25) ovulated in response to hcg while 32% (8/25) ovulated spontaneously during the first 4 days post device removal. in the control group, ovulations occurred randomly. on day 45, animals were ultrasonographed for pregnancy diagnosis. it was recorded a higher percentage of pregnant mares during the first days post treatment in the t group although differences were not statistically significant. in summary, the use of an intravaginal device containing progesterone in a protocol as presented in this study permit an important synchronization of the appearance of ovulatory follicles around day 5 after removal.