A series of 1-substituted 3,4-dihydroisoquinolines has been synthesized and screened for antihypertensive activity in the renal hypertensive rat. The 1-hydrazino homologue 6 and the corresponding acetaldehyde 25 and acetone 23 hydrazones exhibited good activity but were less effective than hydralazine (7). The wide variety of pharmacological activity associated with amidines has been well documented1 and includes such diverse types as antibacterial, hypoglycemic, and antihypertensive activities. l-Amino-3,4-dihydroisoquinolines (3) represent a class of cyclic amidines, some of which have been reported to exhibit cardiovascular and pressor activity2 as well as antitussive and antifibrillatory activity3. We wish to describe the synthesis and antihypertensive activity of several homologues in this series.