The invention relates to N-propargyloxy-phenethyl thioacetic acid amide derivatives of the general formula (I) including the optical isomers thereof and mixtures of such isomers, wherein R1 is hydrogen, alkyl, cycloalkyl or optionally substituted aryl, R2 and R3 are each independently hydrogen or alkyl, R4 is alkyl, alkenyl or alkynyl, R5, R6, R7 and R8 are each independently hydrogen or alkyl, R9 is hydrogen, optionally substituted alkyl, optionally substituted alkenyl or optionally substituted alkynyl, R10 is optionally substituted aryl or optionally substituted heteroaryl, and Z is hydroxy, optionally substituted aryloxy, optionally substituted alkoxy, optionally substituted alkynyloxy, optionally substituted arylthio, optionally substituted alkylthio, optionally substituted alkynylthio, optionally substituted alkylsulfinyl, optionally substituted alkenysulfinyl, optionally substituted alkynylsulfinyl, optionally substituted alkylsulfonyl, optionally substituted alkenylsulfonyl, optionally substituted alkynylsulfonyl or a group —O—CO—R11, —O—CO—O—R11 or —O—CO—CO—O—R11 wherein R11 is hydrogen, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted aryl or optionally substituted heteroaryl. These compounds possess useful plant protecting properties and may advantageously be employed in agricultural practice for controlling or preventing the infestation of plants by phytopathogenic microorganisms, especially fungi