Mortality statistics were analyzed for series of patients with cirrhosis of the liver, disseminated breast cancer, chronic lymphatic leukemia, or myo-cardial infarction. A graphic presentation was utilized, plotting the logarithm of the number of survivors as ordinate and time as abscissa; the slope of the graph was the mortality rate, and the curvature of the curve represented the way in which mortality rate changed with duration of disease. It was found that the 4 diseases analyzed shared an unexpected relationship of mortality rate to duration of disease: the basic mortality rate remained constant during the course of disease; prognosis was neither better nor worse for the patient late in the disease than for the patient early in the disease. In addition patients with myocardial infarction appeared to show accelerated aging; it could not be ascertained whether this also occurred in cancer and cirrhosis, because of their relatively short courses. It was concluded that all of these diseases have in common an alteration of the undefined physiological systems which influence susceptibility to aging and dying, producing an elevated and constant increase in this susceptibility.