We analyzed the characteristics of seven monoclonal antibodies (mAbs) raised against purified HE (hemagglutinin-esterase) glycoprotein of the murine coronavirus DVIM (diarrhea virus of infant mice). Immunocrossreaction of these mAbs with JHM and/or MHV-S suggest that antigenic epitopes of HE of DVIM are similar to those of JHM and/or MHV-S. Four mAbs (1b4, 3a28, 4c19, 10b7), designated as group A mAbs, strongly inhibited both HA and AE activities. On the other hand, three mAbs (5a3, 6a6, 13a4), referred to as group B, had a comparatively weak HA inhibition activity. These results indicate that the antigenic epitopes of this glycoprotein can be classified into at least two groups and that the functional sites of HA and AE activities are similar but not identical. Neutralizing activity was shown in group A mAbs exclusively, suggesting that the ratio of HA and/or AE activities may play important roles in the cell fusion activity of DVIM-infected cells.