The effect of the prostaglandins (PG) D2, E2, F2 alpha and I2 (infusions of 250 ng/min for 10 min into the uterine artery) and relaxin (1 microgram/min) on uterine contractions and on the myometrial and endometrial blood flow to the uterus of ovariectomized, estrogen-primed ewes was investigated. The 85Kr clearance method was used to measure blood flow. PGD2 and PGI2 increased both myometrial and endometrial capillary blood flow, whereas PGE2 and relaxin did not. PGF2 alpha reduced the myometrial blood flow only at a significance level of P less than 0.1 but induced no significant changes in the endometrial flow. PGE2, PGF2 alpha and, notably, PGD2 caused a uterine hypertonus. PGI2 and relaxin did not affect the uterine motility. There is a parallel effect of the investigated substances on the blood flow of myometrium and endometrium but PGD2 induces contractions of the smooth muscle cells in the myometrium while relaxing comparative cells in blood vessels.