The usefulness of thermal inertia mapping for discriminating litholog-ical units was investigated using Sardinia and the Gulf of Orosei as test sites. Software designed forXANDSAT data was modified and improved for HCMM tapes. A first attempt was made to compare the geological cross-section, the topography, the infrared radiance and the thermal inertia along selected profiles of the test site. Thermal inertia profiles appear smooth in comparison with the thermal radiance. The lowest apparent thermal inertia (ATI) was found on granitic and basaltic outcrops of sufficient extent, while ATI is higher on carbonate and dolomitic or moist deposits, Almost every fault is marked by a jump in the ATI, the interval being sometimes of the order of I pixel. This seems to demonstrate the ability of ATI to detect contacts or tectonically disturbed zones with good resolution. It seems more difficult to measure the differences in ATI between homogeneous materials having different lithology. The results of ground surveys and a simulation model of diurnal temperatures of rocks having different thermal inertia are discussed.