The dilatometric behaviour of Na-, K-, NH4- and Ca-clinoptilolite has been investigated. Na-, K- and NH4-clinoptilolite sensibly shrink (from 0.4 to 2.0%) up to about 350 degrees C, while for higher temperatures only very small shrinkages (0.2%) have been detected. These dilatometric behaviours appear to be dominated by dehydration upon heating. Ca-clinoptilolite moderately shrinks up to 300 degrees C (1.0%) and undergoes a more evident shrinkage (2.1%) at higher temperatures. The former shrinkage has been ascribed to dehydration upon heating, the latter higher one to structural damages. The different dilatometric behaviours have been interpreted in terms of the thermal properties of zeolites of the clinoptilolite type,