NEMATOCIDAL COMPOSITION

There are described 2-mercapto-5-pyridyl-1,3,4-oxadiazoles and 2-mercapto-5-pyridyl-1,3,4-thiadiazoles of the formula I in which X represents oxygen or sulphur, R' represents C1-C3-alkyl which is substituted by bromine, fluorine, C1-C3-alkoxy or cyano, C3-C7-alkenyl which is unsubstituted or substituted by halogen; C4-C7-alkynyl which is unsubstituted or substituted by halogen, R represents C1-C3-alkyl, C1-C3-alkoxy which is unsubstituted or substituted by halogen or C1-C3-alkoxy; C3-C7-alkenyl which is unsubstituted or substituted by halogen; C3-C7-alkynyl, C1-C3-alkylthio, halogen, cyano, hydroxyl, amino which is unsubstituted or monosubstituted or disubstituted by C1-C3-alkyl; or aminocarbonyl, and n represents 0, 1, 2, 3 or 4, the process for the preparation of the compounds of the formula I, and novel intermediates of the process. The compounds of the formula I have nematicidal properties. There are described nematicidal agents which contain, as active substance, at least one active substance of the formula I, and furthermore processes for the use of the active substances and the agents in the control of nematodes.