T cell clones derived from the cerebrospinal fluid of patients with multiple sclerosis were investigated for their ability to produce IL2, IL4, IFN gamma and TNF alpha. As controls, liver infiltrating T lymphocyte clones from patients with chronic active hepatitis were used. All CSF clones (both CD4+ and CD8+) produced high amounts of IFN gamma and particularly of TNF alpha. TNF was synthesized in a significantly higher amount than control clones. Moreover, they were capable of secreting IL2 but not IL4. From our results we conclude that CSF-CD4+ T clones could constitute a subset with functional properties similar to those of the Th1/inflammatory cells of the mouse. The unusually high amount of TNF produced by CSF derived T cell clones strongly suggests a significant role for this cytokine in MS immunopathogenesis.