The study deals with 9 women with recurrent abortions who do not possess the blocking factor which is present during normal pregnancy and which inhibits, nonspecifically, a cellular cytotoxicity reaction in vitro. Electrophoresis of the women’s serum revealed an abnormal glycoprotein, migrating in the α-globulin zone, which gives a precipitate with an anti-γ-globulin serum after mercaptoethanol treatment. These last two findings may indicate a possible abortion.