ListBox Font Demo 

unit LBUnit;
interface
uses
  Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
  StdCtrls;
type
  TForm1 = class(TForm)
    ListBox1: TListBox;
    Button1: TButton;
    Button2: TButton;
    Button3: TButton;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure Button3Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;
var
  Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
 ListBox1.Items.LoadFromFile('C:\AUTOEXEC.BAT');
end;
procedure TForm1.Button2Click(Sender: TObject);
begin
 SendMessage
  (ListBox1.Handle,
   wm_SetFont,
   GetStockObject(System_Fixed_Font),
   1);
end;
procedure TForm1.Button3Click(Sender: TObject);
begin
  SendMessage
   (ListBox1.Handle,
    wm_SetFont,
    GetStockObject(ANSI_Fixed_Font),
    1);
end;
end.