A rapid method was developed for the simultaneous determination of hippuric and orotic acid in rennet whey by capillary zone electrophoresis using an uncoated capillary utilizing a 0.04 M amino-2-methyl-1,3-propanediol (AMPD)-N,N-bis(2-hydroxyethyl) glycine (BICINE) buffer (pH 8.8) with UV detection at 254 and 280 nm. Whey proteins were removed by ultrafiltration. The method was evaluated for external, internal and standard addition procedures for both peak areas and peak heights. The use of an internal standard (sorbic acid) eliminated injection errors and gave, when applied to peak areas, the same levels for hippuric and orotic acid in those obtained with high-performance liquid chromatography. Relative standard deviations were 1-2%. Peak heights gave erratic results owing to sample matrix effects on peak widths.