Tryptophan column immunoabsorption therapy is beneficial to the patient with a neuroimmunological disease, but some complications have been attributed to this treatment. There have been some instances of an abrupt shock state along with severe decreases in blood pressure. In regards to this shock state, it has been reported that plasma bradykinin levels increase during tryptophan column immunoabsorption therapy. In this study, we examined the correlation between plasma bradykinin levels and either blood pressure or the levels of its degrading enzymes, angiotensin converting enzyme (ACE) and carboxypeptidase R (CPR) in 6 patients. Increased concentrations of bradykinin were present in the latter half of the therapeutic interval, and plasma bradykinin levels were found to be inversely correlated to CPR activity. The decreased CPR level could augment the activities of bradykinin. We speculate that bradykinin could be responsible for the hypotension occurring in patients during tryptophan column immunoabsorption therapy and that the metabolism of bradykinin could be caused by the decreased activity of CPR.