SELDI-TOF MS profiles for patients with SJIA before and after conventional or MRA treatment. Sera taken before conventional and MRA treatment show similar patterns that are distinct from the post-treatment profiles. Mean spectra of all patients are shown in the 11- to 12-kDa m/z range. Means are compiled from 8 samples before and after conventional therapy and 15 samples before and after MRA therapy, each sample run in duplicate. Spectra were preprocessed as described in the Materials and methods section. MRA, humanized anti-IL-6 receptor monoclonal antibody; SELDI-TOF MS, surface-enhanced laser desorption/ionization time-of-flight mass spectrometry SJIA, systemic juvenile idiopathic arthritis.