Carbonic acid and liquid hot water pretreatments were applied to corn stover. Temperatures ranged from 180 to 220 degreesC; reaction times varied between 2 and 32 min and prereaction carbon dioxide pressure was either 0 or 800 psig. Over the range of reaction conditions tested, it was found that the presence of carbonic acid had an effect of increasing the concentrations of xylose and furan compounds in the hydrolysate that was significant at above the 99% confidence level. Thus there appears to be an increase in the severity of the pretreatment conditions with the presence of carbonic acid. These results are contrary to previously reported results on aspen wood, where the presence of carbonic acid was not found to have an effect on either the xylose or furan concentrations. Although pretreatment conditions were more severe with the addition of carbonic acid, the presence of carbonic acid resulted in a hydrolysate with a higher final pH. Thus it appears that the higher severity conditions reduce the accumulation of organic acids in the hydrolysate. This result was consistent with previously reported work on carbonic acid pretreatment of aspen wood. (C) 2003 Elsevier Ltd. All rights reserved.