Monocyte chemoattractant protein-1 (MCP-1) seems to be involved in the pathogenesis of multiple sclerosis (MS). We found that in unstimulated (PHA(-)) and PHA-stimulated (PHA(+)) peripheral blood mononuclear cells (PBMC), MCP-1 and TNFalpha levels are higher in stable untreated MS patients. Interferon gamma (IFNgamma) is higher in relapsing patients in PHA(-) cultures and in stable patients in PHA(+) cultures. Chronic IFNbeta-1b treatment down-regulates TNFalpha, IFNgamma and MCP-1 production except for TNFalpha in relapsing patients. IFNbeta-1b, in vitro, increases MCP-1, TNFalpha and IFNgamma spontaneous production in all patients. Multivariate analysis suggests that MCP-1 production is dependent from clinical status and not from TNFalpha and IFNgamma production. Logistic regression analysis shows that MCP-1 production is significantly modified by treatment. Further studies are needed to clarify the role of MCP-1 in MS.