  We construct a generic class of models for complex scalar fields -- minimally
coupled to gravity and electromagnetism -- with the property that their
energy-momentum tensor and the electric current vanish for certain massive
configurations. These are electromagnetically and gravitationally {\it stealth
fields}. We shall see that the latter configurations can affect, in addition,
the strength of the gravity-matter and electromagnetic-matter couplings of
other (non-stealth) modes present in the system, which turn out to be
equivalent to the re-scaling the electric charge and the Newton constant (with
a stealth-mass depending factor).
