H2-M3 (M3) is a unique antigen presenting molecule which provides N-formylated peptide to certain type of T cells. Previous observation indicated that NK cell activity is significantly diminished during listerial infection in $H2-M3^{-/-}$ mice. To explore the possibility that M3 expression directly effect on NK cell activity, we measured NK cell activity with or without stimulation of N-formylated peptide on antigen presenting cells. Results indicated that the expression of M3 is not directly influence on NK cell activity. Further study will be focused on the indirect effect of M3 on regulating NK cell activity.