The use of pseudo-random binary sequences (p.r.b.s.) as system input perturbations has become standard practice in the field of identification. Normally, cross-correlation between input and output yields the system impulse response. This is not so if the actual input is a distorted p.r.b.s., the distortion taking tho form of unequal switching delays. This paper describes a theoretical approach which allows calculation of the effects of such distortion on the impulse response estimates. Using these results, a method is devised to remove the effects of a second typo,of distortion, i.e. that which results from unequal input transdvicer time constants. The proposed method allows the removal of secondary peaks but results in increased distortion of parent peaks. A second method, using inverse-repeat sequences, is also investigated. Simulation results are included.