Several hours prior to the first night the child slept in the clean room the child's mother, father, or guardian filled out behavioral rating scales about the child with the assistance of the study's research coordinator. The child also had approximately two tablespoons of blood drawn from an arm and a few inch sample of hair was taken from the back of the child's head. The child and a parent or guardian arrived at The Children's Institute about one half hour prior to the child's normal time of settling for bed for 14 consecutive nights. The child and a parent or guardian slept in the clean room, wearing the provided very clean clothes and sleeping on special mattresses and sheets each night for 14 consecutive nights. The child and parent were observed by a nurse through a window during the time in the clean room. The child and parent participated in regular daytime activities during these 14 days of the study. On the morning after the last night the child and a parent or guardian slept in the clean room a parent or guardian filled out behavioral rating scales with the help of the research coordinator. Approximately two tablespoons of blood were drawn from an arm and a few inch sample of hair was obtained from the back of the child's head, at The Children's Institute or at home.