The role of nitric oxide and its reactive derivatives (NO x ) is well known in the pathogenesis of multiple sclerosis, which is an inflammatory disease while NO x seems to be important in coordinating inflammatory response. The purpose of the present study was to assess serum NO x as one of the nitrogen species and inflammatory parameters in relapsing-remitting multiple sclerosis patients and to compare the effectiveness of various types of disease-modifying therapies that reduce nitric oxide and inflammatory biomarkers. Elevated NO x level was observed in patients who received the first-line disease-modifying therapy (interferons beta-1a and beta-1b) in comparison with the subjects treated with the second-line disease-modifying therapy (natalizumab; fingolimod) and healthy controls without significant differences in C-reactive protein and interleukin-1 beta. A negative correlation was observed between serum NO x level and the duration of multiple sclerosis confirmed in the whole study population and in subjects treated with the first-line agents. Only serum NO x , concentration could reveal a potential efficacy of disease-modifying therapy with a better reduction in NO x level due to the second-line agents of disease-modifying therapy.