NK cells mediate early host defense against viral infection. In murine CMV (MCMV) infection NK cells play a critical role in controlling viral replication in target organs, such as spleen and liver. Until now it has not been possible to directly examine the role of NK cells in MCMV-induced inflammation in situ due to the inability to stain specifically for NK cells in infected tissues. In this study, we describe a method of in vivo fixation, resulting in the first identification of NK cells in situ using NK1. 1 as the marker. Using this method, we characterize the NK1. 1+ cellular component of the inflammatory response to wild-type MCMV in the spleen, liver, and lung of genetically susceptible and resistant mice following ip infection. This study provides the first in situ description of the cellular response mediated specifically by NK cells following MCMV infection.