  An equality of particle and antiparticle gravitational interactions holds in
general relativity and is supported by indirect observations. Here I develop a
method based on high energy Compton scattering to measure the gravitational
interaction of accelerated charged particles. Within that formalism the Compton
spectra measured at HERA rule out the positron's anti-gravity and hint for a
positron's 1.3(0.2)\% weaker coupling to the gravitational field relative to an
electron.
