The surface of lactose particles was modified by a plasma-enhanced chemical vapor deposition process to improve the. flow behavior of the powder. For this, the particulates were treated in a plasma down stream reactor which provides a short (50 ms) and homogeneous exposure to the capacitively coupled RF discharge. The organosilicon monomer hexamethyldisiloxane (HMDSO) was used as a precursor for the formation of SiOx which is deposited on the substrate particle surface. For varying process gas mixtures (O-2/Ar/HMDSO) and RF power applied, the amount of the deposited material was determined gravimetrically after dissolution of the lactose substrate particles and the chemical composition of the accumulated deposition material was investigated by means of attenuated total re. flection Fourier transform infrared (ATR-FTIR) spectroscopy. The concentration of the deposited SiOx relating to the substrate material was found to be in the range of 0.1 wt.%. Based on the ATR-FTIR analysis, the inorganic, i.e. oxidic SiOx fraction of the obtained deposits was shown to be controllable by varying the process parameters, whilst a relatively large amount of organic structures must be considered. (C) 2008 Elsevier B. V. All rights reserved.