Neuropeptides and their receptors are produced and expressed by neuroendocrine tissues and function as neurotransmitters and/or mediators of well-defined hormonal activities in specific tissues and cells. However, neuropeptides and their receptors are also found in the immune system, and various neuropeptides are involved in both systems. In this review we discuss the role of two of these neuropeptides, somatostatin and substance P, with regard to their receptor expression in the human immune system and their role in the diagnosis and treatment of immune-mediated diseases.