The present invention relates to a novel process for preparing known 1-amino-3-phenyluracil derivatives, to novel 1-amino-6-hydroxy-3-phenyldihydro-2,4(1H,3H)pyrimidinedione derivatives of the formula (II) in which R1 is hydrogen, cyano, nitro or halogen, R2 is cyano, nitro, halogen or optionally substituted alkyl or alkoxy, R3 is hydrogen, hydroxyl, mercapto, amino, hydroxyamino, hydrazino, halogen, or one of the radicals —R6, -Q-R6, —NH—R6, —NH—O—R6, —NH—SO2—R6, —N(SO2—R6)2, —CQ1-R6, —CQ1-Q2-R6, —CQ1-NH—R6, -Q2-CQ1-R6, —NH—CQ1-R6, —N(SO2—R6)(CQ1-R6), -Q2-CQ1-Q2-R6, —NH—CQ1-Q2-R6 or -Q2-CQ1-NH—R6, where Q is O, S, SO or SO2, Q1 and Q2 are each independently oxygen or sulphur and R6 is optionally substituted alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl, aryl, arylalkyl, heterocyclyl or heterocyclylalkyl, R4 is hydrogen, halogen or optionally substituted alkyl, and R5 is fluorine- and/or chlorine-substituted alkyl, as intermediates for the 1-amino-3-phenyluracil derivatives, and to a process for preparing the intermediates.