The disclosed derivatives of 1,3-disubstituted 2,4 (1H,3H)quinazolinediones produce vasodilation in experimental animals. The 1,3-disubstitutions include, among others, 1(alky(alkylamino))-, 1-(alkylpiperidyl)-, 3-(alkyl(alkylamino))-, 3-(alkyl(4-phenyl-1-piperidyl)-, and 3-(alkyl(4-phenyl-1piperazinyl))-moieties. In the latter two substituents the phenyl group optionally is substituted with halogeno or loweralkyl groups. Additionally, the compounds optionally are substituted at carbon atoms 5 through 8 of the quinazolinedione nucleus with halogeno, nitro, alkoxy, and alkylamido substituents.