Respiratory syncytial virus (RSV) is the leading cause of lower respiratory tract infections in infants and small children. RSV infection is characterized by significant immunopathology, which is mediated by CD8+ cytotoxic T lymphocytes (CTL). Past studies have suggested that the multiple mechanisms employed by CTLs to eliminate cells may have differential effects on viral clearance and RSV-associated illness. This study seeks to define the contributions of the different CTL effector mechanisms to the clearance of primary RSV infection, as well as their relative impact on the virus-associated immunopathology.