  An integrable asymmetric exclusion process with impurities is formulated. The
model displays the full spectrum of the stochastic asymmetric XXZ chain plus
new levels. We derive the Bethe equations and calculate the spectral gap for
the totally asymmetric diffusion at half filling. While the standard asymmetric
exclusion process without impurities belongs to the KPZ universality class with
a exponent 3/2, our model has a scaling exponent 5/2.
