Special characters, accents and diacritical marks can be entered into an EndNote reference in the following way:

Use the Character Map, supplied with Windows, to copy and paste characters into your EndNote refererence.

Click on Start > Programs > Accessories > System Tools > Character Map

• Select the Arial/Times New Roman or desired font, e.g. for scientific symbols, use Symbols font
• Double-click the character(s) needed.
• Click the Copy button.
• Return to your open EndNote reference, place your cursor where you want the character to go, then click on Edit > Paste
  OR
• You can drag-and-drop characters from the Character map window into your EndNote reference