Studies show that stress is related to changes in both the numbers of white blood cells iin circulation and quantity of antibody in the blood. Moreover, stess is associated with changes in the functioning of immune cells. That is, there is a relatively large decrease in both lymphocyte proliferation and natural killer cell activity in individuals who have experienced stress. There seems to be some connection between the duration of the stress and the amoount of immune change. For example, the longer the stress, the greater the decrease in the number of specific types of white blood cells. It also appears that interpersonal stress, such as divorce or ? death, produce different outcomes compared with the stress due to exams or unemployment. Connections between negative and psychological states, such as anxiety and depression and immune system have been explored, Results suggest that depressed and anxious mood states are associated with decreases in lymphocyte proliferation and natural killer cell activity, as well as changes in numbers of white blood cells and the quantity of antibody circulating in the blood. It also appears that the blody's ability to produce antibody to a specific substance is related to the level of anxiety the individual is experienceing. with more anxiety the less antibody is produced after exposure to the potentially harmful substance. Stress is associated with the activation of several systems, including the hypothalmic ptuitary adrenal axis and the sympathetic nervous system. The activation of these two pathways results in elevated blood levels of specific hormones, namely cortisol and the catecholamines eninepphrine and norep. Blood levels of these hormones are related to immune functioning. For example, actue increases in cortisol and eninephrine are related to decreases in the number of white blood cells in circulation. Lymphocyte profliferation and antural killer cell activiity are also decreased when there are acute > in cor and enpin. The interpretation of these changes in the immune system due to stress is difficult. Even though cell activity is evident in certain diseases, the direct health consequences of such a decrease has not been established. Nevertheless it is clear that stress has an adverse effect on health. probably mediated at tleast in part by the bodys immune system. It is hoped that future research will show how, by reducing stress, we can improve health.