Objective To investigate the relationship between the impairment of immunity and the level of NO in peripheral blood in patients with persistent vegetative state(PVS) resulting from severe brain trauma.Methods The levels of the cortisol and NO in peripheral blood of 12 PVS patients and the control group were tested respectively by radioimmunoassay and nitratase reducing colorimetic method.The phagocytosis and killing of Candida albicans by monocytes were observed.Results The NO content in peripheral blood of PVS group was dropped obviously,but the cortisol level was basically in normal range.Conclusion The suppression of immunity of PVS patients resulted from severe head trauma is related to the decreasing of the NO content in peripheral blood.