Serum from rabbits immunized against normal mouse erythrocytes was administered to mice infected with Plasmodium berghei in six experiments involving a total of 105 mice. These mice were given three to eight daily serum injections, starting shortly before infection or 2 days after infection. Mice receiving this serum experienced severe infections and death earlier than did infected control mice. The blood of immune serum recipients contained high percentages of immature erythrocytes, most of which were parasitized. Normal rabbit serum had no effect upon the course of the infection in the one experiment in which such serum was used.
In two of the six experiments, immune serum recipients showed lower parasitemias than did control mice early in the course of the infection. This response was very transient and these mice later showed higher parasite counts than did the control mice.
Present address: Division of Veterinary Science, College of Agriculture, University of Wyoming, Laramie, Wyoming.