Optimum mixing time and water absorption levels of composite wheat flours were evaluated by response surface methodology. Water absorption was correlated with loaf volume in breadmaking where wheat flour was substituted at 0, 15, or 30% by wheat starch, cassava starch, or cassava flour. The significance of the mixing time was less clear-cut. Baking results showed that the reduced breadmaking potential of wheat flour with partial substitution is not solely a function of gluten dilution. Indeed, loaf volume data showed that the breadmaking potential of a substituted wheat flour is determined by the degree of substitution as well as the type of substitute. Clear differentiation of the substitutes occurs during baking, not at the fermentation stage of the dough. Differential scanning calorimetry showed no drastic differences in the gelatinization properties of the doughs made from substituted flours.