A GC–MS method is reported for the determination of phytic acid based on purification by anion-exchange chromatography, enzymatic hydrolysis of phytic acid to myo-inositol and derivation to trimethylsilyl derivative, with 21 scyllo-inositol as an internal standard. Analytical features of the method are: limit of detection 9 mg l phytic acid, linear 21 working range 18–500 mg l phytic acid, and coefficient of variation 1.9%. The method has been successfully applied to a variety of biological samples: various rat organs (kidney, liver, brain and bone), human plasma and urine and kidney stones. A comparative study of sample treatments, including deproteization, lipid extraction and the presence of a chelator, is also 21 21 reported. Phytic acid amounts found in rat organs ranged from 1.07 g kg for bone to 32.0 g kg for brain. Phytic acid in 21 human plasma was of the order of 0.14 mg l . In kidney stones, phytic acid was found in calcium containing stones.