We describe the general aspects of ion chromatography and how on-line counted ion-exchange techniques can be utilized to determine pyruvic and lactic acids in plasma and vanillymandelic acid in urine. Pyruvate and lactate are extracted from deproteinized plasma by use of an ion-exclusion resin. After elution from the resin, the plasma extract is chromatographed on an anion-exchange column, with 0.66 mmol/L sodium bicarbonate as the mobile phase. The effluent is detected with an electrical conductivity cell. Vanillylmandelic acid is extracted from diluted urine by use of an anion-exchange resin. After elution from resin, the urine extract is chromatographed on an ion-exclusion column, followed by electrochemical detection. We evaluated the procedures for precision, linearity, analytical recovery, intefering substances, and correlation with an established procedure. the combination of a preliminary resin extraction, an ion chromatographic separation, and a conductivity or electrochemical detector results in rapid, specific methods that can be adapted for use in the clinical laboratory. Preliminary data for other organic acids are presented.