The　reaction　of　tetrabutylgermanium　with　ZSM-5　surface　at　230　and　280　degreesC　was　studied　by　means　of　gas　volumetry,　infrared　spectroscopy,　solid-state　NMR　and　elemental　analysis.　The　thermal　stability　and　the　adsorption　properties　of　the　resulting　solids　were　also　determined.　A　condensation　occurred　between　tetrabutylgermanium　and　the　surface　hydroxyl　groups　of　ZSM-5,　being　closly　analogous　to　what　had　been　observed　on　silica　and　mordenite,　The　products　in　the　gas　phase　are　C1-C4　hydrocarbons　formed　by　cracking　of　the　evolved　butane　on　the　highly　acidic　ZSM-5,　and　in　contrast　to　the　report　on　silica　or　mordenite,　a　mixture　of　[(=Si-O)(x)Ge(n-C4H9)(x-4))](x=1,　2,　3)　species　was　formed.　Increasing　the　reaction　temperature　resulted　in　much　more　dealkylated　species.　After　heating　at　450　degreesC,　no　butyl　ligand　remained　on　germanium,　No　modification　of　the　solid　was　detected　by　nitrogen　adsorption,　showing　that　the　zeolitic　structure　was　retained　upon　grafting.　The　modified　materials　show　that　the　adsorption　properties　are　quite　different　from　those　of　the　starting　ZSM-5.　For　example,　2,3-dimethyl　butane　is　totally　excluded　from　the　modified　zeolite　while　the　unmodified　one　easily　adsorbs　it.　n-Hexane　and　2-methyl　pentane　are　also　discriminated　by　this　zeolite　but,　in　this　case,　it　is　due　to　a　decrease　of　the　sorption　rate　at　the　pore　entrance　due　to　steric　hindrances　caused　by　the　grafted　fragments.