High performance liquid chromatography (HPLC) assays are described for measuring the catalytic activities of chorismate-pyruvate lyase andp-aminobenzoate synthase (EC 4.1.3.-), enzymes involved in the ubiquinone and folate biosynthetic pathways, respectively. These assays allow rapid and accurate detection of substrate consumption and product formation. Also depletion of chorismate and the presence of other interfering chorismate utilizing enzyme activities can be observed. The detection limit for the productsp-hydroxybenzoate andp-aminobenzoate is 2.5 ng for both. The suitability of the assays is demonstrated with extracts fromEscherichia coli.