Twenty-five years have passed since J. MILLER'S basic work on the central role of the thymus for the generation of immunological reactivi ty. During this time, the abundance of fascinating literature on the immunological and functional aspects of this organ has been in contrast to the paucity of reports on its role in pathology. The causal or formal pathogenesis even of many of the well-documented pathological fea tures is so far unexplained or at least uncertain. In spite of some concep t...