The role of nitric oxide synthase type-2 (NOS2)-derived nitric oxide (NO) in the pathogenesis of mouse hepatitis virus (MHV)-induced central nervous system disease was examined. Infection of NOS2 knockout ((-/-)) and NOS2(+/+) mice with MHV resulted in similar kinetics of viral clearance from the brain and comparable levels of demyelination. MHV-infected NOS2(-/-) mice displayed a marked decrease in mortality as compared to infected NOS2(+/+) mice that correlated with a significant decrease (P < or = 0.001) in the number of apoptotic cells (determined by TUNEL staining) present in the brain. Confocal microscopy revealed that the majority of cells (>70%) undergoing apoptosis were neurons. These studies indicate that NOS2-generated NO contributes to apoptosis of neurons but not demyelination following MHV infection.