org-babel export latex problem

[Riccardo Romoli <ric.romoli@gmail.com>]

Hi, I'm new of these list and of the org-babel world.
I need to use both LaTeX and R, so I write the R code within an src   
block:

#+begin_src R :results output silent :exports none
library(chemometrics)
library(MASS)
library(lattice)
#+end_src

When I export to LaTex (C-c C-e l) the R code I wrote, this is the  
result:

\begin{verbatim}
library(chemometrics)
library(MASS)
library(lattice)
\end{verbatim}

How could I  not display the result of the R computation? In the org- 
manual (chapter 14 ) I read that what I need should be done using:

:results output silent :exports none

but despite I use this option nothing change.

Do you have any suggestion??

Best
Riccardo