Use the Bold, Italic, Underline and StrikeOut properties to apply different font attributes to the group. Use the Caption property to display different parts of the caption using HTML format. Use the Font property to specify the control's font. Use the Bold property to bold an item. 

The following VB sample bolds all groups:

Private Sub ExplorerBar1_AddGroup(ByVal Group As EXPLORERBARLibCtl.IGroup)
    With Group
        .Bold = True
    End With
End Sub

The following C++ sample bolds all groups:

void OnAddGroupExplorerbar1(LPDISPATCH Group) 
{
	CGroup group( Group ); group.m_bAutoRelease = FALSE;
	group.SetBold( TRUE );
}

The following VB.NET sample bolds all groups:

Private Sub AxExplorerBar1_AddGroup(ByVal sender As System.Object, ByVal e As AxEXPLORERBARLib._IExplorerBarEvents_AddGroupEvent) Handles AxExplorerBar1.AddGroup
    With e.group
        .Bold = True
    End With
End Sub

The following C# sample bolds all groups:

private void axExplorerBar1_AddGroup(object sender, AxEXPLORERBARLib._IExplorerBarEvents_AddGroupEvent e)
{
	e.group.Bold = true;
}

The following VFP sample bolds all groups:

*** ActiveX Control Event ***
LPARAMETERS group

with group
	.Bold = .t.
endwith