A series of 1,3-disubstituted 2,4(1H,3H)-quinazolinediones was prepared from the 3-substituted 2,4(1H,3H)-quinazolinediones by treatment with sodium hydride and the desired alkyl halide in xylene. These compounds showed varying degrees of vasodilation and antihypertensive activity without significant blockade of alpha-adrenergic receptors. 1-[3-(N,N-Dimethylamino)propyl]-3-[3-(4-phenyl1-piperazinyl)propyl]-2,4(1H,3H)-quinazolinedione, which was selected for further studies, was more potent than papaverine in inducing vasodilation and induced a prolonged decrease in systolic blood pressure of hypertensive rats upon oral administration.