Novel mercapto-substituted hydroxyethyl-(triazol-l-yl) derivatives of the formula ##STR1## in which Ar represents optionally substituted aryl,X represents oxygen, sulphur, a direct bond or the groupings --CH.sub.2 --, --CH.sub.2 --CH.sub.2 --, --O--CH.sub.2 --, --SCH.sub.2 --, --O--CH.sub.2 --CH.sub.2 --, and --S--CH.sub.2 --CH.sub.2 --, the hetero atom being bonded to the aryl radical if X represents --OCH.sub.2 --, --SCH.sub.2 --, --O--CH.sub.2 --CH.sub.2 -- or --S--CH.sub.2 --CH.sub.2 -- andR represents hydrogen, optionally substituted alkyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted cycloalkyl, optionally substituted cycloalkylalkyl, optionally substituted aralkyl or optionally substituted phenyl, and their acid addition salts and metal salt complexes are very effective as fungicides and parasiticides. Novel oxiranes of the formula ##STR2## in which Ar and X have the above-mentioned meaning, and their use as intermediates for the synthesis of the mercapto-substituted hydroxyethyl-(triazol-l-yl) derivatives.