Oxazole- and thiazolecarboxamides of the formulae Ia and Ib ##STR1## where the substituents have the following meanings: X oxygen or sulfur;R.sup.1 hydrogen; halogen; substituted or unsubstituted C.sub.1 -C.sub.6 -alkyl, benzyl, cycloalkyl, alkenyl, alkynyl, phenyl, phenoxy or phenylthio; alkoxy; alkylthio; haloalkoxy; haloalkylthio; or a substituted or unsubstituted 5- or 6-membered heterocyclic radical;R.sup.2 formyl, 4,5-dihydrooxazol-2-yl or --COYR.sup.5 ;Y oxygen or sulfur;R.sup.5 hydrogen; cycloalkyl; substituted or unsubstituted alkyl, phenyl, benzyl, alkenyl, cycloalkenyl or alkynyl; a substituted or unsubstituted 5- or 6-membered heterocyclic radical; phthalimido; tetrahydrophthalimido; succinimido; maleiimido; one equivalent of a cation; or--N.dbd.CR.sup.6 R.sup.7 ; R.sup.6, R.sup.7 hydrogen; alkyl; cycloalkyl; phenyl; furyl or together a methylene chain of 4 to 7 members;R.sup.3 hydrogen or substituted or unsubstituted alkyl or cycloalkyl;R.sup.4 hydroxy; alkoxy; substituted or unsubstituted alkyl, cycloalkyl, alkenyl, alkynyl, phenyl or naphthyl; a substituted or unsubstituted 5- or 6-membered heterocyclic radical; or R.sup.3 and R.sup.4 together are --(CH.sub.2).sub.n --Y.sub.p --(CH.sub.2).sub.q --, where n and q are 1, 2 or 3, p is 0 or 1 and Y is oxygen, sulfur or N-methyl, or form a radical of the formula --(CH.sub.2).sub.3 --CO--, and their environmentally tolerated salts,X in formula Ib not being sulfur when R.sup.1 is 3-pyridyl, R.sup.2 is CO.sub.2 CH.sub.2 CH.sub.3 or R.sup.3 is hydrogen, and X in formula Ia X not being sulfur and R.sup.1 not being thien-2-yl when YR.sup.5 is OH, R.sup.3 is hydrogen and R.sup.4 is methyl, processes for manufacturing such compounds and herbicidal agents containing compounds of the formulae Ia or Ib as active ingredients.