Abstract
We present a theory for the effects of disorder on the d.c. and a.c. transport properties of a two-dimensional electron gas in the fractional quantized Hall regime. For the undisturbed correlated Fermi liquid the single-mode approximation is used. Analytical results are given for the magnetic field and the mobility dependence of the gap. It is shown that disorder decreases the excitation gap and that the gap shrinks to zero within a linear behaviour at a critical finite magnetic field. The same occurs at a critical finite impurity concentration.