Quinoa (Chenopodium quinoa) is a valuable source of protein in some parts of South America, and it is likely to be exploited further in both developing and industrialised countries. However, quinoa seeds contain significant levels of saponins which are potential antinutrients. In the present study, the effects of processing on the quantity and composition of saponins in quinoa products were determined, and the biological effects of quinoa grain and cereal products containing high or low levels of saponins were investigated both in vitro and in vivo in the rat. Quinoa saponins were shown to be membranolytic against cells of the small intestine and to cause an increase in mucosal permeability in vitro. Unwashed bitter quinoa caused a significant food aversion and poor food conversion efficiency in rats. However, processing quinoa, during the manufacture of an infant cereal, reduced the concentration and membranolytic activity of saponins, and increased the palatability and nutritional quality of the cereal product to a level similar to that of a wheat-based cereal product.