Abstract: Heat of immersion of zeolite HZSM-5 outgassed at high temperatures and in vacuum have been determined in various organic liquids. The value in terms of kilojoules per avogadro No. of unit cells, Quc, is quite different in each liquid being studied. The order of Quc was found to be n-hexane>n-heptane>n-decane> n-dodecane; benzene < toluene <p-xylene;p-xylene>xylene>xylcnc; methanol< cthanol; and the smallest in cyclohexanc.