Analysis of prosector's findings and results of pathoanatomical studies of 65 cases who had died from sepsis showed that its incidence increased from 0.92% in 1956--1960 to 4.11% in 1971-1974. Along with the well-known typical manifestations of sepsis, a number of its perculiar features associated with application of modern therapeutic methods are considered: the prevailing form of sepsis is pyemia (81.5%), considerable incidence of sepsis following peritonitis and septic thrombophlebitis developing at sites of prolonged catheterization of veins. The significance of staphylococci and Bacillus pyocyaneus, which are resistant to the majority of the available at present antibiotics, as principle pathogenes of modern sepsis is emphasized. A dependence between the localization and size of metastatic foci and the kind of pathogene and nature of its toxines is noted. Among the conditions contributing to the development of sepsis the authors consider a reduction of the immunological reactivity of the organism morphologically characterized in the dead persons studied by the absence in lymphatic follicles of lymphatic nodes and the spleen, of "light" centres, drastic atrophic changes in the thymus gland in the majority of cases, and by slightly manifested phenomena of phagocytosis of microbes in the foci of inflammation. The role of operative and other traumas, the character of preceding diseases and application of immunodepressive therapy in the reduction of the immunological reactivity of the organism is tressed.