In order to enhance and multiply the pharmacological properties of theophylline, the 8-substituted-7-[2-hydroxy-3-(4-acetyl-amino)-fenoxy-propyl]-1,3-dimethyl-xanthine derivatives with various substituents have been synthesized. Their chemical structures have been assessed by IR and H-1 NMR spectroscopy and elemental analysis. The influence of the non-cyclic and cyclic substituents on the thermal and thermo-oxidative behaviours has been followed by thermogravimetry and differential scanning calorimetry. These methods are useful to determine thermal stability, the purity of the compounds and crystallinity. The pharmacological tests have proved their action both on bronchopulmonary and cardiovascular systems.