The cytokine interleukin (IL)‐10 has immune response down‐regulatory properties, which include suppression of the synthesis of pro‐inflammatory cytokines such as interferon (IFN)‐γ and of major histocompatibility complex (MHC) class II expression on monocytes. To further elucidate the involvement of IL‐10 in multiple sclerosis (MS), an enzyme‐linked immunospot assay was adopted to enumerate IL‐10‐secreting mononuclear cells (MNC) in peripheral blood. IFN‐γ secreting MNC were detected in parallel. Levels of IL‐10‐secreting cells were lower in patients with MS compared with other neurological diseases (OND) and healthy subjects. This difference was seen only in patients with untreated MS, and not in those undergoing treatment with IFN‐β‐1b. No differences were observed when subgrouping the patients with MS regarding clinical phase (exacerbation, remission, secondary progression), duration of MS or disability status. Levels of IFN‐γ‐secreting blood MNC did not differ in patients with MS, irrespective of treatment with IFN‐β‐1b, compared with OND and healthy subjects. Patients with MS, but not the two groups of controls, had elevated numbers of IL‐10‐ and IFN‐γ‐secreting cells upon stimulation with MBP compared with culture in the absence of antigen. The data suggest that IL‐10 is decreased in MS and that treatment resulting in its up‐regulation beneficially influence the disease.