One hundred fifty-three ewes were laparotomized. and their uteri were exteriorized and observed for 10 mm for origin and direction of individual uterine contractions. The number of contractions generally averaged between four and seven per minute. At 5 h after the beginning of estrus. 67 percent of the uterine contractions originated near the body of the uterus and moved anteriorly. At 26 h (late estrus). 35 percent of the contractions originated near the uterine body and 42 percent originated near the tubo-uterine junctions. At 48 h (after the end of estrus). 75 percent of the contractions originated at the tubo-uterine junctions and moved toward the cervix. The administration of either 6, 30 or 150 � of estradiol I 7-� between 20 and 40 h after the beginning of estrus prevented the change in direction of contractions. Removing the ovaries during estrus did not prevent the change. When the ovaries were removed from ewes during the luteal phase of the estrous cycle, the administration of either estradiol or estradiol plus progesterone had, in 48 h, initiated uterine contractions that were typical of early estrus. The data suggest that endogenous estrogen initiates the type of uterine motility seen during early estrus, and that declining estrogen secretion is responsible for the change in direction of contractions during estrus. Uterine contractions have been observed in pre-ovulatory estrous ewes in several experiments (Brinsfield and Hawk, 1969: Mann, 1969: Hawk and Echternkamp, 1973: Hawk, 1973). The number of contractions generally averaged five to six per minute, and, in control ewes, the majority of contractions originated near the uterine body and moved toward the oviducts. Other reports suggest that there might be considerable normal variation in the origin and direction of contractions in the reproductive tract. In the estrous rabbit, contractions in the uterus were reported to be continuations of contractions of the oviducts and to move along the uterine horn from the tubouterine junction toward the cervix (Reynolds, 1965). However, in estrous rabbits observed in this laboratory, only half as many uterine contractions moved toward the cervix as moved toward the oviducts (Warren and Hawk, 1971). In ewes, Croker and Shelton (1973) reported that the greatest number of uterine contractions moved toward the oviducts during early estrus but toward the cervix after the end of estrus. A series of experiments was conducted with the ewe to determine the normal changes in the direction of uterine contractions during and soon after the end of estrus, and to investigate the role of ovarian hormones in causing the changes that were found.