Reflection infra-red spectroscopy was used for determining chemical compounds and their transformations within the stone surface. By means of this method chemical changes in the surface of gaize (cretaceous marly limestone) taking place after the application of freezing cycles and interaction with sulfur dioxide were studied. The tests proved that freezing caused irreversible losses of crystal water. The experiments with SO 2 showed that calcium carbonate is transformed into sulfate by two different mechanisms, strongly dependent on the stone water content. -- AATA