WITHIN the last two decades, there have been many attempts to correlate various systemic diseases that have shown vascular lesions. Among these have been periarteritis nodosa, disseminated lupus erythematosus, thromboangiitis obliterans, scleroderma, rheumatoid arthritis, rheumatic fever, dermatomyositis, verrucous endocarditis and serum sickness. In our studies of postmortem and biopsy specimens, we observed certain changes involving the vessels and the collagenous tissue in the aforementioned diseases. These changes, however, were also noted in routine autopsies on patients whose conditions were not diagnosed as any of these. It is our purpose in this paper to point out certain similarities pathologically in these diseases and in the normal aging processes. Further, we will attempt to point out that this "accelerated aging" process of the vessels primarily and of the collagenous tissue secondarily is the basis of the pathogenesis of the so-called diffuse vascular or collagen diseases. In our discussion, we propose the term "panarteriolitis" to describe the process, acute or chronic, involving the entire wall of small and medium-sized blood