  In this paper we investigate the chameleon effect in the different conformal
frames of the Brans--Dicke theory. Given that, in the standard literature on
the subject, the chameleon is described in the Einstein frame almost
exclusively, here we pay special attention to the description of this effect in
the Jordan and in the string frames. It is shown that, in general, terrestrial
and solar system bounds on the mass of the BD scalar field, and bounds of
cosmological origin, are difficult to reconcile at once through a single
chameleon potential. We point out that, in a cosmological context, provided
that the effective chameleon potential has a minimum within a region of
constant density of matter, the Brans--Dicke theory transmutes into general
relativity with a cosmological constant, in that region. This result, however,
can be only locally valid. In cosmological settings de Sitter--general
relativity is a global attractor of the Brans--Dicke theory only for the
quadratic potential $V(\phi)=M^2\phi^2$, or for potentials that asymptote to
$M^2\phi^2$.
