Mice infected with the malarial parasite, P. berghei, become severely anemic within 2-3 weeks, with approximately 10% survival noted by day 24. Transfusion of homologous erythrocytes into these mice on days 14, 15 and 16, completely restored peripheral erythroid parameters to control levels and increased survival to 90%. These data indicate that repeated red cell transfusions into P. berghei infected mice is an effective maneuver which allows for development of host resistance and recovery to an otherwise lethal infection. Complete immunity is further attested by the ability of recovered mice to block the development of malaria upon reinfection with the parasite.