Determination of trace amounts of iodine in food samples was performed by a spectrophotometric method based on the Sandell-Kolthoff reaction catalysed by iodide ions. Samples were decomposed by wet digestion using a HNO₃-HClO₄-H₂SO₄ mixture. The amounts of reagents as well as reaction temperature and time were optimised. The accuracy of the method was tested by examination of the iodine recovery and by analysis of a certified reference material. It was found by the analysis of variance that mineralization had a statistically more significant effect on the assay accuracy than the catalytic reaction itself.