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Diets containing raw soya-beans (RSD) when fed ad libitum cause reduction in growth rate and food utilization, enlargement of the pancreas and increase of its enzyme synthesis. A single meal of raw soya-beans with corn (1 : 9), tube-fed to geese, caused about 90% mortality, while geese, tube-fed with corn alone, did not show any negative response. No mortality occured when geese were fed a similar diet ad libitum. Two-week old chicks were fed ad libitum or by tube, twice a day, similar amounts of RSD or heated soya-bean diet (HSD). While the chicks tube-fed HSD behaved similarly to those feeding freely, the chicks tube-fed RSD collapsed after one week. The thymus and bursa of fabricii were atrophied in the RSD tube-fed chicks. Diets containing increasing amounts of raw soya-bean meal (0, 20%, 42%, and 80%) were fed freely to weanling rats or as one 4 h meal per day. All the rats fed the 4 h meal containing either 42% or 80% raw soya-bean meal died within 3 days; all the others survived. The rats were trained to meal-feeding by gradual reduction of their access to food. The negative effects of the RSD, i.e. reduced food intake and body weight gain, pancreas enlargement, were much more pronounced in the meal-fed rats than in those fed ad libitum. The differences increased by increasing dietary trypsin inhibitor (TI) (raw soya-bean meal).