A central composite design was used to investigate the influence of the cooking conditions (time, temperature and formaldehyde concentration) for wheat straw with formaldehyde-water mixtures on the properties of the pulp obtained (yield and holocellulose, alpha-cellulose, lignin and ethanol-benzene extractives contents) and the pH of the resulting wastewater. A second-order polynomial model consisting of three independent process variables was found to accurately describe the organosolv pulping of wheat straw The equations derived predicted the yield, the holocellulose, alpha-cellulose, lignin and ethanol-benzene extractives contents of the pulp, and the pH of the wastewater with multiple-R, R-2, adjusted-R-2 and Snedecor F values of 0.99, 0.99, 0.99 and 321.33, 0.98, 0.95, 0.92 and 35.01; 0.92, 0.86, 0.78 and 10.68, 0.99, 0.97, 0.96 and 68.19; 0.91, 0.83, 0.80 and 29.68 and 0.97, 0.95, 0.93 and 46.10, respectively. While ensuring a high holocellulose content and low lignin and ethanol-benzene-extractive contents entails using high levels of the process variables involved, a compromise can be made in order to achieve both the previous objectives and a high alpha-cellulose content provided a long cooking time, a high temperature and a low formaldehyde concentration are used - alternatively, a long time, a high formaldehyde concentration and a low temperature can be equally effective and save energy. The yield, pH and holocellulose, alpha-cellulose, lignin and alcohol/benzene extractive contents are more sensitive to changes in the cooking time than they are to modifications of the formaldehyde concentration.