Infectious diseases and other conditions associated with increased production of inflammatory cytokines are often associated with mood and cognitive disturbances. Reichenberg et alArticle report that low-dose endotoxemia, a well-established model of experimental host defense activation, induces a transient increase in anxiety and depressed mood in healthy volunteers, although subjects did not perceive subjective symptoms of illness. Moreover, verbal and nonverbal memory functions were compromised. These effects of endotoxin were significantly correlated with the secretion of cytokines, in particular tumor necrosis factor α, and interleukin 6. These findings suggest that cytokines are important mediators of emotional and cognitive changes in infectious, autoimmune, and neurodegenerative diseases.