A method of combating fungi which comprises applying to such fungi or to a fungus habitat a fungicidally effective amount of a substituted pyrimidine of the formula ##STR1## in which Ar represents optionally substituted phenyl,X represents oxygen, sulphur, sulphinyl, sulphonyl or one of the groups--CH.sub.2 --; --O--CH.sub.2 --; --CHhd 2--O----O--CH.sub.2 --CH.sub.2 --; --S(O).sub.n --CH.sub.2 --; --CH.sub.2 --S(O).sub.n --or --S(O).sub.n --CH.sub.2 --CH.sub.2 --, andY represents on eof the groups ##STR2## where R represents hydrogen, alkyl, alkenyl, alkinyl or optionally substituted aralkyl, andn represents a number 0, 1 or 2,or an acid-additonal salt or metal-salt complex thereof. Most of the compounds are new.