Multiple sclerosis has a tendency to remit during pregnancy, followed by an increase in the risk for disease relapses in the postpartum period. In this communication, preliminary data are presented to indicate that activated peripheral blood mononuclear cells (PBMC) from the postpartum period secrete elevated levels of gamma-interferon (IFN-gamma) relative to those collected during the third trimester. In addition, myelin antigen-specific T cell lines established from the third trimester of pregnancy secrete elevated levels of interleukin-10. The data suggest that the study of the mechanisms underlying natural fluctuations in disease activity during pregnancy and the postpartum period holds promise for a better understanding of factors capable of initiating and regulating remission and exacerbation in MS.