Uteroplacental blood flow is critical for normal fetal growth and development. Uterine and umbilical vessels are under the influence of many factors which could have an impact on fetal well-being. Norepinephrine and 5-hydroxytryptamine are potent constrictors of the uterine and umbilical blood vessels. Isolated ovine uterine artery and umbilical blood vessels were used to study serotonergic and adrenergic mechanisms. The major findings were: (1) 5-hydroxytryptamine induced the hydrolysis of phosphoinositide via activation of 5-HT2 receptors in the ovine umbilical artery; (2) norepinephrine amplified 5-hydroxytryptamine-induced contraction of the ovine uterine artery via activation of [alpha]1-adrenoceptors; (3) [alpha]1-adrenoceptors were heterogenous in the ovine uterine artery and umbilical vein; and (4) activation of protein kinase C was involved in the contractions induced by norepinephrine and endothelin-l in the ovine uterine artery.