Xylanases have a number of industrial uses in baking, modification of animal feed and in the paper industry. Process conditions for paper pulp bleaching generally favour an enzyme that is active at high pH values. Several reports suggested that enzymes such as XynJ isolated from an alkaliphilic Bacillus sp. are highly active at pH values > 9.0, and that single amino acid mutations can increase the alkaphilicity of xylanases but we showed that such enzymes may not have been analyzed under conditions where there was a linear response with respect to substrate concentration. We investigated alteration of the pH profile of a neutral xylanase (optimal temperature 85°C) showing superior performance in bleaching kraft pulp. The gene for the enzyme XynB was cloned from Dictyoglomus thermophilum Rt46.B.1 genomic DNA and a series of mutant libraries were created using error-prone PCR and directed evolution. BadX from Bacillus agaradhaerens and XynB6 were investigated as model enzymes for shifting the pH of the slightly less alkaliphilic enzyme XynB6 to its more alkaliphilic counterpart, BadX, using gene shuffling. Shifts in alkaline activity were found to be minimal and no single mutation altered the pH profile. The alkaline shift seen with BadX was the result of a number of inter-related amino acid changes. We conclude that there may be no point in looking further for enzymes with greater alkaline activity and stability than BadX and close relatives and concentration on improved temperature optima and thermostability may be more appropriate targets for mutagenic alteration.