AbstractThe effects of pretreating wheat straw with gamma‐ray irradiation, ammonium hydroxide, and sodium hydroxide on methane yield, fermentation rate constant, and loss of feedstock constituents were evaluated using laboratory‐scale batch fermentors. Results showed that methane yield increased as pretreatment alkali concentration increased, with the highest yield being 37% over untreated straw for the pretreatment consisting of sodium hydroxide dosage of 34 g OH−/kg volatile solids, at 90°C for 1 h. Gamma‐ray irradiation had no significant effect on methane yield. Alkaline pretreatment temperatures above 100°C caused a decrease in methane yield. After more than 100 days of fermentation, all of the hemi‐cellulose and more than 80% of the cellulose were degraded. The loss in cellulose and hemicellulose accounted for 100% of the volatile solids lost. No consistent effect of pretreatments on batch fermentation rates was noted. Semicontinuous fermentations of straw‐manure mixtures confirmed the relative effectiveness of sodium and ammonium‐hydroxide pretreatments.