The author describes how his interest in the nutritional value of soybeans led to a trail of research that had many ramifications. In an attempt to account for the poor nutritional value of raw soybeans and the beneficial effect of heat treatment, a protein displaying hemagglutinating activity and capable of inhibiting the growth of rats was isolated and characterized. This protein subsequently proved to be an example of a class of proteins that were later referred to as "lectins". Lectins were also isolated from kidney beans and shown to be even more toxic than the soybean lectin. Concurrent studies with the soybean trypsin inhibitors revealed that these proteins inhibited growth by stimulating the secretory activity of the pancreas and could in the long term cause acinar cell adenoma of the pancreas. Acute experiments with human subjects showed that the human pancreas also responded to the stimulatory effects of the so-called Bowman-Birk soybean inhibitor. The studies on soybean trypsin inhibitors were expanded to include a protease inhibitor present in blood, alpha-1-antitrypsin, a deficiency of which leads to emphysema in humans. The mechanism whereby this protein inhibits leucocyte elastase was investigated. On the basis of these results the intratracheal administration of a synthetic peptide inhibitor of elastase attached to albumin microspheres was found to prevent elastase-induced emphysema in hamsters.