The expression of thromboxane (TX) A2 synthase and thromboxane A2 receptor gene in human uterus was investigated by immunoblotting, immunocytochemistry, Northern blot, in situ hybridization, and autoradiographic analyses. Human uterus contains a single immunoreactive protein of 55 kDa that corresponds to the molecular size of human TXA2 synthase. Human uterus also contains a single 2.8-kb TXA2 receptor mRNA transcript and a receptor protein that can bind TXA2 antagonist, 125I-PTA-OH. The immunoreactive TXA2 synthase, TXA2 receptor mRNA, and protein are present in endometrial glands, stromal cells, myometrial smooth muscle, and uterine blood vessels. The TXA2 synthase and TXA2 receptors in different uterine cells varied within as well as between various reproductive states. There were differences in the binding site numbers even between elongated and circular myometrial smooth muscle in all reproductive states except postmenopause. In summary, the data presented demonstrate for the first time that different human endometrial and myometrial cells and uterine blood vessels express TXA2 synthase as well as TXA2 receptor gene. The expression, as well as changes during various reproductive states, suggests that TXA2 could be an autocrine/paracrine regulator of human myometrial contractions, endometrial secretory functions, and intrauterine blood flow and could play a role in the initiation and/or progression of labor in women.