ABSTRACT: In the present study we have investigated the influence of pregnancy on the induction and development of experimental autoimmune encephalomyelitis (EAE) in rabbits in relation to the time of gestation. Randomly bred rabbits were immunized with encephalitogenic bovine brain homogenate in complete Freund's adjuvant before or during pregnancy. The appearance of EAE was delayed and occurred only after delivery, abortion, or fetal resorption. The incidence of the disease was lower and the duration longer. The levels of antibodies to myelin basic protein, an autoantigen of EAE, as measured by solid phase radioimmunoassay, were lower in the pregnant rabbits as compared to the nonpregnant animals. The suppressive influence of pregnancy on the induction and the development of EAE confirms previous reports demonstrating amelioration of autoimmune diseases and other immunological reactions during the second half of human pregnancy. This effect might be partially attributed to the increased level of alpha-fetoprotein (AFP) and/or other pregnancy-associated factors in maternal serum.