Abstract: The invention provides a method for determining the effect of a biological agent comprising contacting a cell culture with a biological agent. The cell culture of the invention contains a culture medium containing one or more preselected growth factors effective for inducing multipotent central nervous system (CNS) neural stem cell proliferation. The cell culture also contains, suspended in the culture medium, human multipotent CNS neural stem cells that are derived from primary CNS neural tissue that have a doubling rate faster than 30 days.