A series of substituted 2-piperidino-4-amino-6,7-dimethoxyquinazolines was synthesized and screened as potential antihypertensive agents. The hypotensive effect of all the new compounds was studied after intravenous administrations in urethane-anesthetized normotensive rats. The furoylpiperazine moiety in the prazosin molecule could be replaced by a more stable substituted piperidine group without loss of the blood pressure lowering activity. However, the nature of the substituent profoundly influenced the hypotensive potency as well as the duration of the hypotensive action. Some of the new compounds were found to be as potent as prazosin. On the basis of potency and the duration of the hypotensive action in the anesthetized rats, five of the most promising compounds were selected for further studies. Each of these agents exerted an antihypertensive effect upon oral administrations in conscious spontaneously hypertensive rats. At small doses, the new compounds appeared to be somewhat less potent than prazosin, but at the higher doses of 10-100 mumol/kg, two of them appeared to be even more efficacious antihypertensive agents than prazosin.