  We demonstrate a contradiction of quantum mechanics with local hidden
variable theories for continuous variable quadrature phase amplitude
(``position'' and ``momentum'') measurements, by way of a violation of a Bell
inequality. For any quantum state, this contradiction is lost for situations
where the quadrature phase amplitude results are always macroscopically
distinct. We show that for optical realisations of this experiment, where one
uses homodyne detection techniques to perform the quadrature phase amplitude
measurement, one has an amplification prior to detection, so that macroscopic
fields are incident on photodiode detectors. The high efficiencies of such
detectors may open a way for a loophole-free test of local hidden variable
theories.
