High xylan content of dissolving pulp could have some undesirable detrimental effects in the conversion process to viscose rayon. Crude xylanase preparations of Aureobasidium pullulans and Thermomyces lanuginosus were tested for their abilities,to remove hemicellulose and lignin from sulfite pulps in conjunction with hydrogen peroxide in one-stage or multistage bleaching to dissolving pulp. Three different types of sulfite pulps (unbleached, low viscosity, and oxygen-delignified) were used to evaluate the xylanase pretreatment. A. pullulans xylanase showed a greater affinity for sulfite pulps than T. lanuginosus xylanase as indicated by the release of reducing sugars from the pulps and biobleaching experiments. In the one-stage bleaching with hydrogen peroxide, pretreatment of unbleached and low viscosity pulps with A. pullulans xylanase contributed to an additional increase in brightness by 4.0 and 3.2 points and a 4 and 3% reduction in kappa number, respectively. Biobleaching of unbleached sulfite pulp with A. pullulans enzyme preparation produced dissolving pulp with superior quality over the control of OD1EoD2P-bleached pulp. The hemicellulose content (expressed as alkali solubility S-18) of the xylanase-prebleached dissolving pulp was reduced by 6-8%, whereas brightness was increased by 2.2 points; Although T. lanuginosus xylanase produced some biobleaching effect in the one-stage hydrogen peroxide treatments, there was no obvious improvement in brightness after a full five-stage bleaching to dissolving pulp. Therefore the evaluation of different xylanases in biobleaching would require their testing also in; complete multistage bleaching experiments, especially where very high brightness levels are desired as in the case of dissolving pulp.