Nonlinear distortion was investigated in 367 new hearing aids. Among the first group of instruments examined, the level of harmonic distortion present at 500, 700, and 900 Hz was studied, together with the frequency and extent of maximum distortion. Ear-level instruments generally yielded lower distortion values than did body types. The frequency of maximum distortion tended to fall below 1000 Hz for body-worn instruments, while the frequencies at which maximum distortion occurred for the ear-level hearing aids were predominandy above 1000 Hz. The variability in total distortion exhibited within groups of fifteen instruments each of identical make and model was examined among a second group of instruments. Results for this procedure, which employed 60 dB SPL input signals and full-on acoustic gain settings, indicated that, although most of the instruments exhibited distortion products of less than 10% throughout their frequency range, total nonlinear distortion in excess of 20% was not uncommon among these hearing aids.