The nitrogen solubility of soy products was determined in water, phosphate buffer, and buffer with urea and/or mercdptoethanol. The water solubilities in decreasing order were: minimally heat processed flours, isolates, heat processed flour, and concentrates. Heat treatment of soy flours increased hydrogen, hydrophobic, and disulfide bonds. The insolubility of isolates and concentrates was due mostly to hydrophobic and hydrogen bonding. The in vitro digestibilities in decreasing order were: isolates, concentrates, heat processed flour, and minimally heat processed flours. PER decreased as disulfide bonding increased except in minimally heat-treated flours. For products with little or no inaccessible disulfide bonding, digestibility increased as hydrogen and hydrophobic bonding increased.