Changes in the trypsin inhibitor activity (TIA) of faba beans (Vicia faba L. Major) were investigated after beans were soaked in distilled water, citric acid, and sodium bicarbonate solutions. The soaking solution was discarded. The effect of cookingdiscarding both soaking and cooking solutionswas also studied. Finally, a dry-heating process was examined. Soaking treatment produced a slight decrease of trypsin inhibitor activity. Cooking the presoaked seeds brought about the total or partial removal of TIA, depending on the soaking solution used. TIA was partially removed after dry-heating. Trypsin inhibitor activity analyses were completed with 28-day biological trials for raw and dry-heated faba beans. For 21 and 28 days of experimental time food intake, protein intake, and weight gain were similar for rats fed raw and dry-heated faba beans. However, after 28 days protein efficiency ratio (PER) and food transformation index (FTI) improved in rats fed dry-heated faba beans compared with those fed raw faba beans. This was related to lower TIA values found in dry-heated faba beans. This work was supported by Spanish Comision Interministerial de Ciencia y Tecnologia (CICYT) ALI 94-1419-E and ALI 96-0480, and is part of the BSc of C.D.-P. and Ph.D. of M.F. J.F. is grateful to the European Union for financial support through an individual bursary (AIR3-BM93-1118). Peer reviewed