In multiple sclerosis (MS), the signs of inflammation that can be detected in the central nervous system are not mirrored by unequivocal markers of activation of the immune system in the periphery. We performed a serial monitoring of serum amyloid A protein (SAA), a major acute phase reactant, in peripheral blood of patients with relapsing-remitting MS over a 3-month period. Patients were monitored in parallel with gadolinium-enhanced magnetic resonance imaging (Gd-MRI) of the brain. The results show that signs of ongoing peripheral inflammation, reflected by elevations of SAA levels, can be detected in MS patients.