A central composite design was used to investigate the influence of the cooking conditions (time, temperature and acetone concentration) for wheat straw with acetone-water mixtures on the properties of the pulp obtained (yield and holocellulose, alpha-cellulose, lignin and ethanol-benzene extractable contents) and the pH of the resulting waste water. 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 predict the yield, the holocellulose, alpha-cellulose, lignin and ethanol-benzene extractable contents of the pulp, and the pH of the waste water with multiple-R, R-2 and adjusted-R-2 high values. The process variables must be set at low values to ensure a high yield and pH. Conversely, if high holocellulose and alpha-cellulose contents and low lignin and ethanol-bezene extractable contents are desired, then a high temperature (200 degrees C), an intermediate-to-long cooking time (95-100 min), and a low-to-intermediate acetone concentration (55-60%) must be used.