The thermal behaviour of ciprofloxacin, its hydrochloride and two copper (II) compounds of ciprofloxacin was studied by thermogravimetry (TG), differential scanning calorimetry (DSC), evolved gas analysis (EGA) and IR spectroscopy. In all the compounds studied, profound differences in the carboxylic nu(C=O) absorption were found after heating, which can be explained by the rearrangement of the hydrogen bonds.