A 3-yr study demonstrates that commercially acceptable reproductive performance can be achieved in breeding sheep following the application of a fluorogestone-acetate- (FGA-) impregnated intravaginal sponge and pregnant mare's serum gonadotrophin (PMSG) treatment to induce a synchronized estrus under field conditions. Overall fertility, prolificacy and fecundity levels of 76%, 1.92 and 148%, respectively, resulted from breeding at the synchronized estrus, and 94%, 1.86 and 175%, respectively, due to breeding at the synchronized and subsequent estruses in the breeding (fall) season. In the nonbreeding (spring) season, these responses were 51%, 1.73 and 88%, respectively, at the synchronized estrus, and 63%, 1.61 and 109%, respectively, due to breeding at the synchronized and subsequent estruses. Significant farm-to-farm variation was observed with reproductive performance ranging from 77 to 100% for fertility, 1.45 to 2.74 for prolificacy, and 134 to 274% for fecundity in the estrous season. There were no significant differences among farms after synchronization and breeding during the anestrous season. Key words: Sheep, synchronization, fluorogestone acetate, pregnant mare's serum gonadotrophin, season, farm flocks.