The influence of relative humidity (RH) on carbon dioxide sorption at 105 Pa in wheat gluten films (WGF) was investigated in the range of 0-96% RH at 25 degrees C. The amount of water sorbed by these protein based films reached up to 60% of the dry weight at 96% R.H. Carbon dioxide sorption increased with water content, ranging from 2.8 x 10(-4) to 1.9 x 10(-2) mol Pa-1 m(-3) respectively at 0% and 96% R.H. This behavior was tentatively explained on the grounds that sorbed water enhanced carbon dioxide accessibility to protein active sorption sites. The dependence of both the solubility and the diffusivity coefficients of CO2 and O-2 on WGF water content explains the very good permselectivity of these films observed at high RH values (22 at 93% RH and 25 degrees C). (c) 2005 Elsevier Ltd. All rights reserved.