The Jayme-Wise and diglyme-HCl methods for extracting cellulose from plant material for stable-isotope analysis differ considerably in ease of use, with the latter requiring significantly less time and specialized equipment. However, the diglyme-HCl method leaves a small lignin residue in the crude cellulose that may affect stable-isotope values, whereas a-cellulose produced by the Jayme-Wise method is relatively pure. We examined whether adding a bleaching step to the diglyme-HCl method could produce cellulose of comparable purity to a-cellulose by comparing the yield, percent carbon, and carbon (δC-13) and oxygen (δO-18) stable isotope ratios of the two celluloses. We tested each method on the wood of five species that differ in ease of delignification, Eucalyptus maculata Hook., E. botryoides Sm., E. resinifera Sm., Pinus pinaster Ait. and Callitris glaucophylla J. Thompson & L.A.S. Johnson, as well as the foliage of C. glaucophylla. For hardwoods such as the eucalypts, the diglyme-HCl method without bleaching produced cellulose with δC-13 and δO-18 ratios similar to a-cellulose. For the softwood, C. glaucophylla, 3 h of bleaching with acidified chlorite following treatment with diglyme-HCl produced cellulose with δC-13 and δO-18 ratios similar to a-cellulose. Bleached and unbleached crude celluloses and a-cellulose of P. pinaster were similar in δO-18, but not δC-13. Both types of crude cellulose produced from the foliage of C. glaucophylla had significantly different isotope ratios from a-cellulose. Overall, the diglyme-HCl method, with or without bleaching, appears to be a simple, fast method for extracting a-cellulose from hardwoods for stable isotope analyses, but its suitability for softwoods and foliage needs to be evaluated depending on the species.