Abstract Ethyl β-D-glucosiduronic acid was isolated from the urine of male and female rats, and from the urine of an adult male human alcoholic. The isolation and structural studies were carried out by apparently general gas phase procedures for the study of glucosiduronic acids. The methods involve isolation from urine by extraction and ion exchange chromatography, and identification by gas liquid chromatography and by the combined technique of GLC-mass spectrometry.