The 8-substituted bis-xanthine derivatives with various substituents have been synthesized taking in the view the previous results with xanthine derivatives, exhibiting enhanced and multiplied pharmacological properties in respect with those of theophylline. Their chemical structures have been assessed by IR, UV and H-1 NMR spectroscopy and elemental analysis. The influence of the non-cyclic and cyclic substituents on thermal and thermo-oxidative behaviors 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 that their action both on bronchopulmonary and cardiovascular systems depends on the nature of the substituent.