Concentrated acid hydrolysis of cellulosic material results in high dissolution yields. In this study, the neutralization step of concentrated acid hydrolysate of conifer pulp was optimized. Dry conifer pulp hydrolysis with 55 % H2SO4 at 45 A degrees C for 2 h resulted in total sugar yields of 22.3-26.2 g/L. The neutralization step was optimized for solid Ca(OH)(2), liquid Ca(OH)(2) or solid CaO, mixing time, and water supplementation. The highest hydrogen yield of 1.75 mol H-2/mol glucose was obtained with liquid Ca(OH)(2), while the use of solid Ca(OH)(2) or CaO inhibited hydrogen fermentation. Liquid Ca(OH)(2) removed sulfate to below 30 mg SO4 (2-)/L. Further optimization of the neutralization conditions resulted in the yield of 2.26 mol H-2/mol glucose.