Normal human urine contains many anions and cations. Ionic concentrations in urine have classically been determined by spectrophotometry of color reactions, flame emission spectrophotometry, atomic absorption spectrophotometry, high performance liquid chromatography, or potentiometry with ion-specific electrodes. Capillary ion electrophoresis (CIE) is a form of capillary electrophoresis which uses the differential electrophoretic mobility of ions to perform a separation of an ionic mixture. Various salts can be added to urine specimens to abnormally elevate ionic concentrations and interfere with either immunoassay urine drug screening procedures or gas chromatographic/mass spectrometric confirmation techniques. Application of CIE for the direct detection of endogenous anions and anionic adulterants in human urine specimens was the purpose of this investigation. CIE was performed using a Waters Quanta 4000 Capillary Electrophoresis System with either direct or indirect ultraviolet absorption detection at 254 nm. CIE of 30 random normal urine specimens and 21 urine specimens suspected of adulteration was performed. Duplicate aliquots were assayed by CIE and by colorimetric technique for nitrite. Sixteen specimens had elevated concentrations of nitrite and/or nitrate. The correlation coefficient between nitrite CIE and colorimetric results was 0.9895. Three specimens had detectable concentrations of chromate and were suspected of being adulterated with "Urine Luck," an adulterant found to contain chromate. Two specimens suspected of being adulterated with bleach were found to only contain chloride, sulfate, and phosphate. CIE is applicable to forensic analysis of urine anion concentrations. CIE can easily quantitate numerous endogenous anions and offers a method to detect and/or confirm anion adulteration of urine specimens.