 Thirty-three days after the last dose of chloroquine, volunteers in groups 1 and 2 will have controlled human malaria infection CHMI by the bites of five mosquitoes infected with PfSPZ of the Pf NF54 strain. If 75 of volunteers in group 1 are protected against this homologous Pf CHMI, volunteers in groups 3 and 4 will have CHMI by the bites of five mosquitoes infected with the heterologous Pf NF135.C10 strain 75 days after the last dose of chloroquine. 