A series of 4-(3, 4-dihydroxyphenyl)-1, 2, 3, 4-tetrahydroisoquinoline derivatives showed potent DA 1 agonistic activities. We investigated the structure-activity relationship of the racemic compounds of this series. 4-(3, 4-Dihydroxyphenyl)-7-methanesulfonamido-1, 2, 3, 4-tetrahydroisoquinoline (43) was identified as a potent renal vasodilator with activity almost equal to that of YM435 (1).