4-Amidino derivatives and quaternary salts of tetrahydro-1,4-benzodiazepines were synthesized and evaluated for antihypertensive activity in conscious rats by the oral route. Included in this study were derivatives of 1,2,4,5,6,7-hexahydropyrrolo[3,2,1-jk][1,4]benzodiazepine and 1,2,3,4,8,9,10,11-octahydro[1,4]diazepino[6,5,4-jk]carbazole in which the 1 and 9 positions of tetrahydro-1,4-benzodiazepine are linked by an ethylene and a cyclohexenyl chain, respectively. Four compounds exhibited marked blood pressure lowering activity (greater than 50 mmHg) at doses of 75 mg/kg. Further study indicated that these compounds are effective by impairing transmission in the sympathetic nervous system.