Fifty-seven Duroc, 41 Landrace and 38 Yorkshire purebred sows in d 10 to 53 of pregnancy were aborted to synchronize estrus by using prostaglandin F₂α (PGF₂α). Breed differences in time between injection of two 10-mg doses of PGF₂α and return to estrus were observed in these three breeds of pregnant sows during two breeding seasons. Duroc sows returned to estrus .9 d faster (P<.01) than Yorkshire and 1.3 d faster (P<.01) than Landrace sows. Seasonal differences were also observed. The mean days from injection to estrus were 1.8 d fewer (P<.01) for the spring season than in the fall season. All sows expressed estrus 5 to 11 d after injection. Normal gestation, parturition and piglet survival were observed in the sows after the treatment. Genetic differences in response to induced abortion and return to estrus could have implications in planned breeding and farrowing systems.