The Maillard, or nonenzymatic, browning reaction between carbonyl and amino groups is a common reaction in foods which undergo thermal processing. The Maillard reaction is a desirable consequence of many industrial and domestic processes and is responsible for the attractive flavor and brown color of some cooked foods. An early recognized consequence of the Maillard reaction was the destruction of some essential amino acids, such as lysine. More recently, research interest has focused on the production of toxic and antinutritive compounds. This review examines the nutritional and toxicological consequences of the Maillard reaction in light of the findings of such research. In particular, the effect of Maillard reaction products on the digestion, absorption, and excretion of nutrients is considered. The cytotoxicity, mutagenicity, and immunochemical aspects of selected Maillard reaction products are also examined and suggestions are made for future areas of investigation.