The aim of our study was to investigate the following: (1) the level of CSF lactate in patients with relapsing-remitting multiple sclerosis (RRMS) compared to healthy subjects; (2) the potential value of CSF lactate to predict disease severity and progression; (3) the relationship between CSF lactate levels and both t-tau and neurofilament light (NFL) protein. Here, NEFL is linked to relapsing-remitting multiple sclerosis.