  A Nordtvedt effect at cosmological scales affects the acoustic oscillations
imprinted in the cosmic microwave background. The gravitational baryonic mass
density of the universe is inferred at the first peak scale from WMAP data. The
independent determination of the inertial baryonic mass density through the
measurement of the deuterium abundance in the framework of standard big bang
nucleosynthesis leads to a new constraint on a possible violation of the strong
equivalence principle at the recombination time.
