  The linear conductance of the a small metallic tunnel junction embedded in an
electromagnetic environment of arbitrary impedance is determined in the
semiclassical limit. Electron tunneling is treated beyond the orthodox theory
of Coulomb blockade phenomena by means of a nonperturbative path integral
approach. The frequency dependent conductance is obtained from Kubo's formula.
The theoretical predictions are valid for high temperatures and/or for large
tunneling conductance and are found to explain recent experimental data.
