Human ability to experience negative and positive emotions has an evolutionary perspective and the presence of feelings designed to influence behavior should thus be reflected in physiological and immune interactions. The complex interactions between the immune system and the central nervous system have been studied extensively in schizophrenia and depression. On the other hand, effects of positive human emotions, especially happiness, on physiological parameters and immunity have received very little attention. Emotions are intimately involved in the initiation or progression of cancer, HIV, cardiovascular disease, and autoimmune disorders. The specific physiological responses induced by pleasant stimuli were recently investigated with the immune and endocrine systems being monitored when pleasant stimuli such as odors and emotional pictures were presented to subjects. The results revealed that an increase in secretory immunoglobulin A and a decrease in salivary cortisol were induced by pleasant emotions. The mechanisms by which positive as opposed to negative states are instantiated in the brain and interact with the immune system are not yet understood. The present review investigates relations among physiological measures of affective style, psychological well-being, and immune function. There is data to support the hypothesis that individuals characterized by a more negative affective style poorly recruit their immune response and may be at risk for illness more so than those with a positive affective style. Future research is needed to expand our knowledge of the physiological and immune interactions of positive emotional states and their beneficial effects on health.