A class of novel heterocyclicacetonitriles which is useful in the control of fungi, especially bitunicate asci and unitunicate asd, has been discovered. These compounds are of the general formula: ##STR1## wherein Ar.sub.1 and Ar.sub.2 are substituted or unsubstituted aryl groups; Het is a six-membered nitrogen-containing heterocyclic ring; n is the integer 2 or 3; and the agronomically acceptable enantiomorphs, add addition salts and metal complexes thereof.