  The issue of the physical equivalence between the Einstein and Jordan
conformal frames in Jordan-Brans-Dicke (JBD) theory is revised. Scalar-tensor
theories equations are not invariant with respect to conformal transformations
if one uses the same "gauge" fixing in Jordan and Einstein frames. We hope to
have clarified some eventual obscure issues associated to the concept of
conformal invariance of relativistic theories appearing in the literature, in
particular the relationship between Jordan and Einstein frames.
