  A simultaneous Electroweak and QCD fit of electroweak parameters and parton
distribution functions to HERA data on deep inelastic scattering is presented.
The input data are neutral current and charged current inclusive cross sections
measured by the H1 and ZEUS collaborations at the ep collider HERA. The
polarisation of the electron beam was taken into account for the ZEUS and H1
data recorded between 2004 and 2007. Results are presented on the vector and
axial-vector couplings of the Z boson to u- and d-type quarks. The values are
in agreement with Standard Model predictions. The results on a_u and v_u
represent the most precise measurements from a single process.
