The damage produced by 20–40 keV He+, N+and Zn+irradiations of Si, GaAs and GaP at 50°K has been measured in-situ by 1.0–1.5 MeV He+channeling techniques along both (111) and (110) directions. It has been found that the measured damage increases significantly when the analysing beam is misaligned by angles up to 0.36 ψ1. The magnitude of the effect decreases with cascade damage fraction and total disorder level. Significant deviations occur between the measured disorder and that predicted by binary collision theory. It appears that the measured damage is the result of the collision cascade initiating inter-and/or intra-cascade processes which can result in a much larger number of displaced atoms than predicted.