Which structure in the human brain produces most cerebrospinal fluid?

The choroid plexus produces most cerebrospinal fluid in the human brain.

Choroid plexuses are specialized networks of blood vessels and epithelial cells located in the brain’s four ventricles. Their cells filter and actively secrete components from blood to form cerebrospinal fluid, commonly abbreviated CSF. This clear fluid cushions the brain and spinal cord, helps maintain a stable chemical environment, and carries away some waste products.

The choroid plexus is found in both lateral ventricles and in the third and fourth ventricles. Although CSF can also be produced in smaller amounts by other parts of the ventricular system, the choroid plexus is the principal source.

A common mix-up is confusing the choroid plexus with the blood–brain barrier. The plexus contributes to the blood–CSF barrier, which controls movement between blood and CSF, while the blood–brain barrier regulates exchange between blood and brain tissue. CSF circulates through the ventricles and around the central nervous system before being returned to the bloodstream.