The realization, in the past decade or so, that bidirectional communication between the central nervous system and the immune system was likely has sparked an explosion of interest in the roles certain cytokines, particularly the proinflammatory cytokine interleukin-1 beta (IL-1 beta), might play in the brain. The observation that IL-1 type I receptor was expressed in highest density in the hypothalamus was of significance in identifying a role for IL-1 beta in neuroendocrine modulation. However, the finding that receptor expression was also high in the hippocampus, an area of the brain which plays a pivotal role in memory and learning, has led to uncovering a role for IL-1 beta in cognitive function. There is now a great deal of evidence suggesting that IL-1 beta plays a significant role in hippocampal synaptic function, and the possibility that IL-1 beta may trigger some of the detrimental changes in certain neurodegenerative diseases is currently being assessed. The review addresses some of the issues relating to the role of IL-1 beta in the brain, specifically in the hippocampus.