We studied the expression of chemokine receptors CCR1, CCR2, CCR3, CCR5, and CXCR3 on CD4 and CD8 positive T cells, and on CD14 positive monocytes in blood from 10 patients with relapsing-remitting multiple sclerosis (MS) at initiation of interferon (IFN)-beta treatment, after 1 month and after 3 months of treatment. It was found that the expression of CXCR3 on CD4+ and CD8+ T cells was significantly reduced after 3 months of treatment. The expression of other receptors was unaltered. Since CXCR3 cells are enriched in cerebrospinal fluid (CSF), and are detected in lesion material in MS this may represent an important mode of action of interferon-beta in MS.