Astrocytes are the most abundant cells in the central nervous system (CNS). Astrocytes provide a variety of biological functions, such as supporting endothelial cells involved in blood-brain barrier formation, providing nutrients to neurons, maintaining extracellular ion balance, and promoting repair in the CNS. Astrocyte conditioned medium-serum free (ACM-sf) has been widely used to support the growth of neurons and endothelial cells in culture. ACM has also been shown to protect neurons from corticosterone-induced damage. ACM-sf is a liquid medium prepared from primary human astrocyte cultures by using astrocyte medium (Cat #1801) without serum conditioned for 48 hours. The medium is sterile filtered and has a pH of 7.4 when equilibrated in an incubator with an atmosphere of 5% CO2/95% air.