  The photon asymmetry in the reaction p(\vec{\gamma},\pi^{0})p close to
threshold has been measured for the first time with the photon spectrometer
TAPS using linearly polarized photons from the tagged-photon facility at the
Mainz Microtron MAMI. The total and differential cross sections were also
measured simultaneously with the photon asymmetry. This allowed determination
of the S-wave and all three P-wave amplitudes. The low-energy theorems based on
the parameter-free third-order calculations of heavy-baryon chiral perturbation
theory for P1 and P2 agree with the experimental values.
