2,4-pyrimidinedione derivatives of formula (I) having high antiviral activity against wild-type and mutant HIV-1 and low toxicity are useful for treating AIDS (I) wherein: R1 is a C¿6-10? aryl or C3-10 heteroaryl group optionally having one or more substituents selected from the group consisting of halogen, C1-6 alkyl, C1-6 alkyl substituted with one or more halogen atoms, C3-6 cycloalkyl, cyano, nitro, hydroxy, thiohydroxy, azido, C1-6 alkoxy, oximino, C1-3 alkyloximino, O-(C1-6 alkyl)-substituted oximino, C-1-6 alkylcarbonyl, C3-6 cycloalkylcarbonyl, hydroxymethyl, azidomethyl, C1-6 alkoxymethyl, C1-6 acyloxymethyl, carbamoyloxymethyl, aminomethyl, N-(C1-3 alkyl) aminomethyl, N,N-di(C1-3 alkyl) aminomethyl, carboxy, C1-6 alkoxycarbonyl, aziridine, amino, hydroxyethylamino, cyclopropylamino, C1-6 alkylamino, di(C1-6 alkyl) amino, trifluoroacetamido, C1-6 acylamido, carbamoyl, hydroxyethylcarbamoyl, cyclopropylcarbamoyl, C1-6 alkylcarbamoyl, di(C1-6 alkyl) carbamoyl, aminocarbamoyl, dimethylaminocarbamoyl, hydrazino, 1,1-dimethylhydrazino, imidazolyl, triazolyl and tetrazolyl; a tetrahydropyridyl or piperidyl group optionally substituted with a C1-6 alkyl or C1-6 alkoxycarbonyl group; a tetrahydropyranyl group; or a tetrahydrofuryl group; R?2¿ is hydrogen, halogen, nitro, cyano, C¿1-3? alkoxycarbonyl, C1-3 alkylamino, di(C1-3 alkyl) amino, C1-3 alkylcarbamoyl, di(C1-3 alkyl) carbamoyl, C1-6 alkyl, C3-6 cycloalkyl or benzyl; R?3 and R4¿ are each independently hydrogen, halogen, hydroxy, cyano, nitro, amino, acetamido, trifluoroacetamido, azido, C¿1-3? alkyl, C1-3 alkyl substituted with one or more halogen atoms, C1-3 alkoxycarbonyl, carbamoyl, C1-3 alkylcarbamoyl, di(C1-3 alkyl) carbamoyl or C1-3 alkoxy; A is O or S; and Z is O, S, C=O, NH or CH2.