Vapors of n-hexane (I) and n-heptane (II), each adsorbed at 20degreesC on, and thermally desorbed from HY or HZSM-5 (using linear or stepwise temperature program over 20-400degreesC), produced desorption isobars with one (HY) or three (HZSM-5) inflection points, resp., and one minimum (I: 150 degreesC; II: 137degreesC) or two minima (I: 114 and 196degreesC; II 47 and 198 degreesC) in the corresponding isobar derivative curves. The observed total sorption capacities for I and II were 164 and 154 mg/g for HY and 107 and 101 mg/g for HZSM-5, resp. The desorption profiles were successfully fitted with formula derived from the Langmuir adsorption model and values of the standard desorption enthalpy and entropy were estimated. Two types of adsorption sites in HZSM-5 differing in the adsorption entropy were suggested to account for the two minima in the isobar derivative profiles.