Vanishing hall and longitudinal resistances in bilayer two-dimensional electron systems at v(T)=1

Longitudinal and Hall resistances have been measured in a bilayer two-dimensional electron system at v(T) = 1 with equal but oppositely directed currents flowing in the two layers. In the limit of zero temperature, both of these resistances are observed to drop to zero. This supports the prediction of an excitonic superfluid state existing at this total filling factor.