  The analysing power measurements for the p(pol)p -> pp eta reaction studied
in this dissertation are used in the determination of the reaction mechanism of
the eta meson production in nucleon-nucleon collisions.
  Measurements have been performed in the close-to-threshold energy region at
beam momenta of p(beam)=2.010 and 2.085 GeV/c, corresponding to the excess
energies of Q = 10 and 36 MeV, respectively. The experiments were realised by
means of a cooler synchrotron and storage ring COSY along with a cluster jet
target. For registration of the reaction products the COSY-11 facility has been
used. The identification of the eta meson has been performed with the missing
mass method.
  The results for the angular dependence of the analysing power combined with
the hitherto determined isospin dependence of the total cross section for the
$\eta$ meson production in the nucleon-nucleon collisions, reveal a
statistically significant indication that the excitation of the nucleon to the
S_{11} resonance, the process which intermediates the production of the eta
meson, is predominantly due to the exchange of a pi meson between the colliding
nucleons.
  The determined values of the analysing power at both excess energies are
consistent with zero implying that the eta meson is produced predominantly in
the s-wave at both excess energies.
