The contractile response of the equine uterus to different oxytocin doses administered intramuscularly during oestrus was investigated in 5 reproductively normal mares given sequential doses of 5, 10, 20 and 40 USP oxytocin. The time from oxytocin administration to onset of response ranged from 5-22 min, but was not affected by dose (P=0.6) or mare (P=0.9).