Objective: Members of the tumor necrosis factor (TNF) receptor superfamily play a major role in the pathogenesis of multiple sclerosis. To elucidate the role of TNF receptors, in 53 relapsing-remitting multiple sclerosis patients, we measured the TNF receptor 1 and receptor 2 (TNF-R1 and TNF-R2) mRNA levels in peripheral blood leukocytes in natural history (n = 27) and during administration of interferon (IFN) β-1a (n = 26). Methods: Every 3 months for the duration of 1 year peripheral blood leukocytes were investigated by quantitative reverse transcription polymerase chain reaction. Every 6 months, MRI scans of the brain were analyzed semiquantitatively. Results: At baseline, clinical expanded disability status scale score and TNF-R1 mRNA level were correlated. In the therapy group, the difference between T2 lesion load at baseline and after 12 months correlated negatively with the difference between TNF-R1 mRNA level at baseline and after 12 months. Subcutaneously applied IFN β increased the amount of TNF-R1 mRNA, but partly decreased the amount of TNF-R2 mRNA in clinically and subclinically defined responders to therapy after 1 year compared to baseline. Conclusion: This result might support the notion that due to different signal transduction properties of both receptors in the natural course of multiple sclerosis, TNF-α signaling in leukocytes via TNF-R1 might be beneficial, but detrimental via proinflammatory TNF-R2: part of the therapeutic efficacy of current first-line standard therapy with IFN might be due to the modulation of signal transduction pathways.