A series of laboratory studies was conducted to test the effect of the inclusion of soy flour in bread at the levels of 2, 4, 6, 8, 10 and 12%. The farinographic tests showed that several changes occurred with the incorporation of soy flour to the wheat flour, such as an increase in water absorption and weakening of the dough, and a decrease in the dough developing time. The mixing time remained unchanged up to the level of 8% substitution. Higher levels produced an increasing stickiness of the dough that made its handling more difficult. Soy-containing breads were slightly darker than wheat bread with a score of 71 points (scale 100) for the 12% level of substitution. The texture became coarser with increasing substitution of soy flour. Starting with the level of 4% of soy flour a volume decrease was observed, but this was corrected by the addition of 0.5% sodium stearoyl-2-lactylate (SSL). At the levels of 10 and 12% of soy flour, SSL was not effective in preventing the reduction of volume. The chemical composition of bread showed a regular increase in its protein content from 13.4, to 18% in the bread containing 12% soy flour. The protein efficiency ratio of bread improved from 1.17 for the wheat bread, to 2.13 for the bread containing 6% soy flour (casein, 2.54). Our results confirm the observation made by other workers in that the inclusion of soy flour in bread improves both the protein concentration and quality of this basic food.