  We investigate the suppression of superconducting transition temperature in
granular metallic systems due to (i) fluctuations of the order parameter
(bosonic mechanism) and (ii) Coulomb repulsion (fermionic mechanism) assuming
large tunneling conductance between the grains $g_{T}\gg 1$. We find the
correction to the superconducting transition temperature for 3$d$ granular
samples and films. We demonstrate that if the critical temperature $T_c > g_T
\delta$, where $\delta$ is the mean level spacing in a single grain the bosonic
mechanism is the dominant mechanism of the superconductivity suppression, while
for critical temperatures $T_c < g_T \delta$ the suppression of
superconductivity is due to the fermionic mechanism.
