Circadian rhythms are daily oscillations of multiple biological processes. Recently, relationships between circadian rhythms and immune functions have also been described. In a mouse sepsis model, the death rate due to lipopolysaccharide (LPS)-induced endotoxic shock was found to be dependent on LPS administration as determined by circadian time. In humans, a pronounced inflammatory response to endotoxemia differs depending on whether it is daytime or night-time: Levels of tumor necrosis factor-alpha and interleukin-6 were higher during the night. Therefore, it is reasonable to assume that circadian rhythms influence not only organ dysfunction and the prognosis induced by LPS, but also the therapeutic effect of anti-LPS therapy such as Polymyxin-B direct hemoperfusion. We herein postulate the concept that it is important to discuss septic shock treatment in terms of whether or not the treatment is adjusted for the optimal time window as determined by circadian rhythms.