openssh unix dev - Jan 2000 - Can't open display error

Hi,

 I get this message on the latest Debian potato for i386.

--> ssh -f localhost xterm
sb at localhost's password: 
--> xterm Xt error: Can't open display: 

 There does not seem to be any doc on the topic.
 Also, all my xterm proc do not appear under sshd in pstree,
 so I guess there is something wrong there too?

 Sergio

P.S. I am not subscribed to the list, so please copy the reply to me.