A classification on the basis of time-course effect is proposed to describe the pleiotropic actions of interleukin-1 (IL-1) on the central nervous system (CNS); two main time-frames, minutes-to-days and days-to-years, are distinguished. The former includes the central aspects of acute-phase response with fever, altered food and water intake, sleepiness, sickness behaviour and neuroendocrine changes. Apart from stress response triggered by immune-inflammatory stimuli, the concept that IL-1 mediates other types of stress is also reviewed, showing that the cytokine may have a role in mediating hypothalamic responses to restrain stress and nociceptive stimuli. The days-to-years time-frame includes several CNS disorders accompanied by inappropriate and/or sustainedly elevated IL-beta production: ischaemia, Alzheimer's disease, HIV-related dementia and experimental allergic encephalomyelitis-multiple sclerosis. In all cases, IL-beta is not envisioned as an aetiological factor, but it contributes significantly to the maintenance of disease state. Current and perspective therapeutic approaches involving the modulation of IL-beta production and effects are briefly discussed.