Varhaug KN, et al. - This research was designed to assess the potential of serum neurofilament light chain (NF-L) and chitinase 3-like 1 (CHI3L1) as serum biomarkers for clinical use in the follow-up of patients with relapsing-remitting MS (RRMS). For subclinical MRI activity and treatment response in RRMS, serum NF-L could be a promising biomarker. Serum NF-L could offer an alternative to MRI monitoring for subclinical disease activity, in clinically stable patients.