LDIF with umlauts

Hallo,
i want to add umlauts (like ä,ö, etc...) in my LDAP. 
It's no problem if I use JNDI,
but if I want to add umlauts in LDIF-Data with the LDAPADD Command
I always get this error message:
ldap_add: Invalid syntax
additional info: sn: value #0 contains invalid data
Thanks for helping,
Fritz Bayer