  The e^+p neutral-current deep inelastic scattering differential
cross-sections $d\sigma/dQ^2$, for Q^2 > 400 GeV^2, $d\sigma/dx$ and
$d\sigma/dy$, for Q^2 > 400, 2500 and 10000 GeV^2, have been measured with the
ZEUS detector at HERA. The data sample of 47.7 pb^-1 was collected at a
center-of-mass energy of 300 GeV. The cross-section, $d\sigma/dQ^2$, falls by
six orders of magnitude between Q^2 = 400 and 40000 GeV^2. The predictions of
the Standard Model are in very good agreement with the data. Complementing the
observations of time-like Z^0 contributions to fermion-antifermion
annihilation, the data provide direct evidence for the presence of Z^0 exchange
in the space-like region explored by deep inelastic scattering.
