In their reports in the 29 February issue ("Land clearing and the biofuel carbon debt," J. Fargione et al., p. 1235, and "Use of U.S. croplands for biofuels increases greenhouse gases through emissions from land-use change," T. Searchinger et al., p. 1238), the authors do not provide adequate support for their claim that biofuels cause high emissions due to land-use change. The conclusions of both papers depend on the misleading premise that biofuel production causes forests and grasslands to be converted to agriculture. (Letters)