Radiative corrections to the parity-violating asymmetry measured in elastic
electron-proton scattering are analyzed in the framework of the Standard Model.
We include the complete set of one-loop contributions to one quark current
amplitudes. The contribution of soft photon emission to the asymmetry is also
calculated, giving final results free of infrared divergences. The one quark
radiative corrections, when combined with previous work on many quark effects
and recent SAMPLE experimental data, are used to place some new constraints on
electroweak form factors of the nucleon
