Abstract: A series of novel 7-(D.alpha.-aminophenylacetamido)- and 7-(D-.alpha.-hydroxyphenylacetamido)- .DELTA..sup.3 -cephem derivatives have been prepared wherein a heterocyclic thiomethyl moiety is located at the 3-position of the molecule. These compounds are useful as antibacterial agents for the treatment of diseases caused by Gram-positive and Gram-negative bacteria. Preferred members include 7-(D-.alpha.-hydroxyphenylacetamido)-3-(3-carbamoyl-1,2,4-triazol-5-yl)thi omethylceph-3-em-4-carboxylic acid and 7-(D-.alpha.-hydroxyphenylacetamido)-3-(2-carboxymethoxy-methyl-1,3,4-thia diazol-5-yl)thiomethylceph-3-em-4-carboxylic acid. Alternative methods of preparation are provided for these compounds, including various synthetic routes leading to the required novel heterocyclic thiol intermediates.