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Astrocytes are ubiquitous in the brain and have multiple functions. It is becoming increasingly clear that they play an important role in monitoring the neuromicroenvironment in CNS and in information processing or signaling in the nervous system in normal conditions and respond to CNS injuries in a gradual and varied way. It is still debated whether such reactions are beneficial or detrimental. It was believed that reactive astrogliosis observed in most neurological disorders may regulate the removal of toxic compounds produced by damaged neurons and support neuronal growth by releasing trophic factors. However it was also suggested that astrocytes contribute to a decline of neurologic function, for example by accumulation and release of excitotoxic aminoacids after ischemia and oxidative stress, formation of epileptogenic scars in response to CNS injury and metabolism of protoxins to potent toxins. In a number of metabolic diseases astrocytes, not neurons, may be the primary target. The astrocyte's role in normal and pathological conditions will be discussed in the light of recent information about their metabolism, receptor distribution and release. [ABSTRACT FROM AUTHOR]