This contract will evaluate substances in cotton rats for their clinical therapeutic or prophylactic potential to safely treat or prevent paramyxovirus (respiratory syncytial virus, parainfluenza virus type 3, and measles virus)-induced infectious diseases of humans. In addition, the models will be used to study the disease pathogenesis of these viruses and host responses to infections caused by these viruses. When appropriate, these models will also be used for a limited amount of vaccine evaluation and pharmacokinetic studies.