The synthesis of the acetoxymethyl (AOM), pivaloloxymethyl (POM), and phthalidyl (PHTH) esters of 7-[D-(-)-2-amino-2-phenylacetamido]-3-[5-methyl-(1,3,4-thiadiazol-2-yl)thiomethyl]-3-cephem-4-carboxylic acid (1a), a broad-spectrum semisynthetic cephalosporin antibiotic, is described. These esters were examined as potential orally active antibiotic prodrugs. The superior oral absorption of the three esters relative to the unesterified parent, 1a, is demonstrated by differential blood levels as well as measurement of the rate at which doses of the ester leave the gastrointestinal tract and appear in the urine. A study of the decreased stability of the three esters relative to 1a at pH 4.5, 6.5, and 7.5 is also presented.