Intracellular production of TNFalpha and IL-2 after stimulation with phorbol myristate/ionomycin was flowcytometrically measured in CD4(+) T cells from peripheral blood (PB) and cerebrospinal fluid (CSF) of 29 patients with multiple sclerosis (MS), and 16 with other inflammatory and 41 with other non-inflammatory neurological diseases. In CSF, the percentages of CD4(+)TNFalpha(+)IL-2(-)T cells were significantly higher in patients with MS than either of the controls, whereas no difference was found in CD4(+)TNFalpha(+)IL-2(+)T or CD4(+)TNFalpha(-)IL-2(+)T cells. The increase was more pronounced at relapse than in remission. No significant change was detected in PB. These findings suggested that CD4(+)TNFalpha(+)IL-2(-)T cells are intrathecally upregulated in MS.