The sympathetic nervous system innervates immune organs and, when activated, releases its signaling molecules in the vicinity of immune cells. The released molecules include the "classical" transmitters norepinephrine and epinephrine and the co-transmitters ATP and adenosine. Immune cells express various adrenergic and purinergic receptors that are sensitive to these molecules, and the production of immune/inflammatory mediators (cytokines, chemokines, and free radicals) is modulated by activation of these receptors. Notably, the production of tumor necrosis factor-alpha, interleukin-6, -10, and -12, and the chemokine macrophage inflammatory protein 1alpha and the production of the free radical nitric oxide, produced by the inducible nitric oxide synthase, have been shown to be altered by activation of these receptors. Alterations in the production of the immune mediators may contribute to the development of various diseases. On the other hand, novel experimental therapies based on the modulation of adrenergic or purinergic receptors on immune cells are emerging. Such approaches may have beneficial effects in limiting tissue injury and suppressing symptoms in certain pathophysiological states.