2-Amino-pyrimidininone derivatives possessing serotonin-antagonistic and antihistaminic properties. Compositions containing these compounds as the active ingredient. Method of treating subjects suffering from diseases and/or disorders associated with the release of neurotransmitters, in particular, a method of treating subjects suffering from sleep disorders with 2-aminopyrimidinone derivatives substituted with a 4-bis(aryl)methylene-1-piperidinyl group; and a method of treating subjects suffering from psychotic diseases and/or disorders with 2-aminopyrimidinone derivatives substituted with a 4-arylcarbonyl-1-piperidinyl, 4-benzazoyl-1-piperidinyl, 4-benzazolyl-1-piperazinyl or 4-indolyl-1-piperidinyl, 4-benzo[b]furanyl-1-piperidinyl or 4-benzo[b]thienyl-1-piperidinyl group.