A review of the arguments in favor of the so-called immunologic theory of aging is presented. Recent evidence, showing that arteriosclerosis, one of the main aging diseases, also has important immunological or autoimmunological factors, is in favor of this theory. It can be shown that in several aspects, this theory can be reduced to a ‘differenciation theory’ of the aging process. The macromolecules of the intercellular matrx – collagen, elastin, proteoglycans, and especially strctural glycoproteins – may play an important role in this process and may often become the targets of autosensitization phenomena related to loss of self-discriminating capacity in the aging immunocompetent system. There may be a link here between the autoimmune diseases of connective tissue and the immunological mechanisms of aging.