Alkaline pretreatment of wheat plant (WP), including its grains and straw, was investigated under different conditions in order to enhance biomethane production at mesophilic temperature. Alkaline pretreatment was performed using 8% (w/v) NaOH solution at different temperatures (0, 25, 50, 75 and 100 degrees C). The best improvement in the yield of methane production was achieved by pretreatment at 75 degrees C for 60 min, giving a methane yield of 404 ml g(-1) VS. The highest glucose content was also obtained under this pretreatment. The cumulative methane yield for pretreated WP at 25, 50 and 75 degrees C increased the methane yield around 47.5%, 40.8% and 54.5% higher than that of the untreated WP, respectively, while pretreatment at 0 and 100 degrees C was not effective in improving the biogas production. Qualitative analysis of pretreated WP using Scanning Electron Microscopy and Fourier Transform Infrared showed the reduction of crystallinity as well as the removal of surface layers of lignin and hemicellulose. (C) 2013 Elsevier Ltd. All rights reserved.