The cellulase-free xylanase from an alkalophilic thermophilic Bacillus was stable at pH 7.0 to 10.0 at 50 degrees for 3 days. At 60 degrees the enzyme showed a decrease in stability with a half- life of 3 h. Addition of various additives had no effect on the enzyme stability at 60 degrees. Glycine (0.5M) increased-the enzyme half-life 6-fold at pH 7.0 to 9.0 and at 60 and 70 degrees. Xylan could offer protection against thermoinactivation of the xylanase at pH 7.0 and 8.0 at 60 degrees and only a marginal increase at pH 9.0 at 70 degrees was observed.