Maize stover, rice straw, oil palm fronds and sugarcane bagasse were treated with the white-rot fungi Ceriporiopsis subvermispora, Lentinula edodes, Pleurotus eryngii, or Pleurotus ostreatus at 24 degrees C for 0-6 weeks. The fungi increased total gas production from oil palm fronds by 68-132%, but none of the fungi improved the in vitro rumen fermentability of maize stover. C. subvermispora and L. edodes increased total gas production of sugarcane bagasse by 65-71%, but P. eryngii and P. ostreatus decreased it by 22-50%. There was a linear relationship (P < 0.05) between the proportion of lignin in the original substrate and the increase in in vitro gas production observed for C. subvermispora and L edodes treatments (R-2 = 0.92 and 0.96, respectively). It is concluded that C subvermispora and L. edodes have a particularly high potential to improve the nutritive value of highly lignified ruminant feeds. (C) 2012 Elsevier Ltd. All rights reserved.