Gas chromatographic analysis of urinary indole-3-acetic acid as the trifluoroacetyl derivative of its methyl ester was carried out. A 10 ml portion of urine sample, acidified and saturated with sodium chloride, was extracted with benzene. After methylation with diazomethane in ether, indole-3-acetic acid was converted to the trifluoroacetyl derivative. Indole-3-butyric acid was used as an internal standard. This method was applied to human urine samples and the results showed the presence of 1.5-3.5 mg/day or 0.31-2.50 μg/mg creatinine of indole-3-acetic acid in normal urine, while the excretion of indole-3-acetic acid was higher in leukemia, gastric cancer, and phenylketonuria.