<p>In a hermetically sealed hood provided with recycle and recovery apparatus a labelled compound is obtained by adsorbing and releasing a gaseous radioisotope under vacuum in a reaction system incorporated with vials containing adsorbents thereby to bring said gas into contact with a compound to be labelled and to recover the gas remaining in the system by adsorbents or reacting agents, and removing a vial of products and a recovery vial of unreacted gases by sealing under vacuum. The gaseous radioisotope used in said preparation of the labelled compound is itemized by applying the principle of adsorption and release and the removal by seal under vacuum mentioned above to capillary apparatus connected with said gas ampoule and a plural of recovery vials.</p>
