Objective To explore the effect of leptin on cytokine production by PBMCs obtained from MS patients either in acute (relapse) or in stable (nonrelapse) phase of disease. Methods PBMCs were collected from 25 untreated acute MS patients, 11 stable MS patients and 20 healthy controls. PBMCs were cultured either with RPMI-1640 alone or with leptin (1.25 nmol/ml), phytohemagglutinin (PHA) ( 100 μg/ml), and leptin + PHA. 72 h later the supernate of the culture medium were collected and stored at -70℃. The pro-inflammatory cytokine (IFN-γ) concentration were determined using an enzyme-linked immunosorbent assay ( ELISA), and the anti-inflammatory cytokine (IL-4) concentration were investigated by radioimmunity methods. Results Our data showed that leptin induced IFN-γproduction by PBMCs of patients in an acute phase of disease but not in a stable phase or in healthy controls. Moreover, we found that PHA induced IL-4 production by PBMCs of patients in an acute phase of disease, but leptin inhibited this ability of PHA. Conclusion Leptin can affect on pro- and anti-inflammatory cytokine production by PBMCs collected from MS patients, may be this connected with leptin increase the susceptiveness of MS.