Malaria is a sickness passed from one person to the other by the bite of a mosquito. In areas of frequent malaria infection, children may develop natural protection against malaria and they are less likely to become sick or die from it as they age. The purpose of this study is to investigate the body's natural protection against malaria in children by testing their blood. This information may help investigators develop a malaria vaccine. The Navrongo Health Research Centre is conducting this study in Ghana. Three hundred healthy children between the ages of 1 and 5 years will participate in the study for 12 months. Study procedures will include 7 field worker visits to check on the child's health and obtain a blood sample. Every two months, a blood sample will be taken from each child to test it for strength against malaria. Whenever a child is sick, the child will be tested for malaria.