This paper describes the use of in-situ FTIR to monitor the growth of VO2 thin films on SiO-precoated glass from VCl4 and H,O under APCVD conditions. It is shown that the amount of H2O introduced during the various reaction conditions can affect the intensity of HCl only in high excess. This observation is attributed to the operation of a possible surface reaction mechanism. The data presented here also suggest that the direct monitoring of the HCl bands might be an excellent process of providing a method of process control. (c) 2007 Published by Elsevier B.V.