A standard diagnostic blood smear from a drop of blood will be carried out on 20 study subjects once per month. One malaria-positive subject from among the 20 will be asked to donate 5cc of blood, also no more frequently than once per month. The blood will be placed in a water-jacketed heated membrane feeding device that will be positioned on top of a cage of mosquitoes. The mosquitoes are attracted to the warmth and drink the blood through the artificial skin-like membrane. The goal of the research is to study the infected mosquitoes. No studies will be carried out on the human subjects. The point of human subjects involvement is to obtain the naturally malaria-infected blood for feeding of mosquitoes. After blood feeding, the mosquitoes are held in an environmental chamber for one week, at which time they are dissected to count numbers of malaria parasites developing on the mosquito stomach wall. This number constitutes the quantitative phenotype, and we extract genomic DNA from the carcass for genetic marker typing, which constitutes the genotype. Genetic linkage analysis identifies markers near genes that control parasite number, thus resistance or susceptibility to parasite infection.