  We report measurements of the Coulomb-blockade current in resistively
isolated (R_{Isol} >> h/e^{2}) tunnel junctions for the temperature range 60mK
$We report measurements of the Coulomb-blockade current in resistively isolated
($R_{Isol}\gg h/e^{2})$ tunnel junctions for the temperature range 60mK < T <
230mK where the charging energy E_{c} is much greater than the thermal energy.
A zero-bias resistance R_{0} of up to 10^{4}R_{T} (the tunnel resistance of the
bare junction) is obtained. For eV << E_{c}, the I-V curves for a given
R_{Isol} scale as a function of V/T, with I \propto V^{\alpha (R_{Isol})} over
a range of V. The data agree well with numerical calculations of the tunneling
rate that include environmental effects.
