DNA was ozonized in solution and the reaction was followed with polarimetry and with iodimetry. Polarimetry was used to determine the molar ratio DNA/O(3) when the DNA optical activity vanishes completely. At a molar ratio DNA/O(3)=2.3 the supramolecular structure of DNA collapses completely. Instead, iodimetry shows that the ozonolysis proceeds until all the nucleobases have been destroyed, an event which occurs at a molar ratio DNA/O(3)=1.1. The ozonolysis of DNA was also followed spectrophotometrically. DNA is reactive with ozone also in the solid state, as fixed bed. Clear indication about its oxidation derives from the FT-IR spectra from polarimetric measurements and from thermal analysis performed by thermogravimetric analysis (TGA), differential thermogravimetric analysis (DTG) and from differential thermal analysis (DTA). Particular remarkable is the fact that RNA has been found much less reactive toward ozone in the solid state than DNA.