gnus fetches only headers

[kguy]

I have the following line in my category file
((Latex high nil ("comp.text.pdf" "comp.text.tex")) 
(Programming high nil ( "comp.lang.c"  "gnu.gcc" "gnu.gcc.help"
"gnu.cvs.help")) 
(Linux high nil ("comp.os.linux.misc" "comp.os.linux.networking"
"comp.os.linux.portable" "comp.os.linux.setup" "comp.os.linux.x"
"uk.comp.os.linux")) 
(Emacs high nil ("gnu.emacs.gnus" "gnu.emacs.help" "gnu.emacs.bug"
"comp.emacs" "comp.emacs.xemacs" "gnu.chess" "gnu.emacs.gnews"
"gnu.emacs.lisp")) 
(default false nil nil))
When entering J-s gnus only retieves the headers of the messages
contained in the group. When I try to read the content of the message
I get the message 
"message marqed for download"
How to I get gnus fetching all the messages contained in group in a
category?
I would like to download really all messages since disk space is not a
concern.
thanks for any hint
Guy
-- 
                Guy-Armand Kamendje
           Graz University of Technology