The role of serotonin (5-HT) in blood pressure (BP) regulation was reviewed. Central and peripheral 5-HT receptors can be divided into three receptor subtypes: 5-HT1 (5-HT1A, 5-HT1B, 5-HT1C), 5-HT2 and 5-HT3 receptors. The selective agonists and antagonists of these receptor subtypes are useful for investigating the BP regulation by 5-HT. The central 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) produced hypotension and decreases in sympathetic nerve activity (SNA). This suggests that central 5-HT may cause decreases in both BP and SNA via 5-HT1A receptors. Since the 5-HT2 receptor antagonist ketanserin, which has an antihypertensive effect, decreased SNA and the 5-HT2 agonist 1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) increased SNA, central 5-HT2 receptors may be connected with the 5-HT-induced increases in both BP and SNA. On the other hand, ketanserin's antihypertensive effects via its 5-HT2 receptor blocking action in the vascular system indicates that peripheral 5-HT may contribute to the initiation or the maintenance of elevated vascular resistance in several forms of hypertension including essential hypertension. However, ketanserin also possesses α1-adrenoceptor blocking action, and its precise antihypertensive mechanism has not been established. Further study of the antihypertensive mechanism of ketanserin will help clarify the precise role of 5-HT in BP regulation.