Expression of mRNA for interleukin-6, interleukin-6Delta3, and interleukin-6Delta5 was detected in placental tissue (second and third trimesters of pregnancy) and spleen of mice immunized with sheep erythrocytes in high dose. We hypothesize that translation of mRNA yields proteins capable of binding to individual subunits of the interleukin-6 receptor and possessing effector functions.