Uterine contractions may play an important role in the transportation of spermatozoa towards the site of fertilisation in the oviduct of mares. M-mode ultrasound was used to measure the number, amplitude and duration of uterine contractions in each uterine horn and the uterine body of oestrous mares for four minutes before and four minutes after either coitus, or the artificial insemination of either 80·0 ml of fresh semen or 10·0 ml of fresh semen. The direction of the uterine contractions in each uterine horn and the uterine body was measured before and after coitus. Coitus and the insemination of 80·0 ml semen significantly increased the total number, mean amplitude and mean duration of contractions in all parts of the uterus. The insemination of 10·0 ml of semen did not affect the total number or the mean duration of contractions in the uterine horns. Their mean amplitude was increased, but largely owing to the results from one mare; it also did not affect the contractions in the uterine body. There was no significant difference between the percentage of contractions moving in a cervicotubal or tubocervical direction after coitus in any part of the uterus examined.