What service is using a port?

["John M. Purser" <jmpurser@comcast.net>]

I apologize.  I know this was a thread a while back and I believe it was on
this mailing list but now I can't find it.  I'm getting this error message
from samba:
[2003/08/17 12:15:26, 0] lib/util_sock.c:open_socket_in(789)
  bind failed on port 139 socket_addr = 0.0.0.0.
  Error = Address already in use

so I'm trying to find out what's using port 139 that wasn't doing so
yesterday.

Thanks,

John Purser