1. Single, thin-walled, acephalic cysts from cotton rat donors were inoculated intraperitoneally into the experimental hosts, and cyst weights were taken at several intervals after infection.

2. Specific rodents are the principal hosts of the hantaviruses including the hispid cotton rat (Sigmodon hispidus) in southern Florida, which is the principal host of Black Creek Canal virus., The deer mouse (Peromyscus maniculatus) in Canada and the Western United States is the principal host of Sin Nombre virus.