using character like ä, ü in statements

Hello.

I want to get a result from a table which contains ä,ü etc. in the tablename. With tools like toad i get a result. But if i want to get it from sqlplus an error occured.
Has anybody a tip for me.
The statement i want to use:

select * from TAB_ZÄHLER;

The error-message:

ORA-00911: Ung³ltiges Zeichen Received on Wed Mar 27 2002 - 05:38:34 CST