The inescapable chronic exposure of cellular and extracellular matrix molecules to reducing sugars which can initiate the Maillard reaction in vivo suggests that the fundamental aging process might be mediated by the Maillard reaction. An attempt to explain aging on the basis of the Maillard reaction, however, raises a number of conceptual questions. These questions are formulated below as a basis for a theory of aging based on the Maillard reaction.