The most ubiquitous method of measuring the attenuation of hearing protection devices (HPDs) is that of real-ear attenuation at threshold (REAT). Such tests, which evaluate the hearing thresholds of human subjects both with and without the HPDs in place, have often been criticized for measurement artifact and inappropriate test conditions. We examined two of the more common alleged REAT problems; masking of the occluded thresholds due to amplified physiological noise and the possible errors resulting from extrapolating low sound level performance tests to the high sound levels in which HPDs are typically worn. An ear canal mounted subminiature microphone was used to measure physiological noise in occluded and unoccluded test conditions as well as to measure the insertion loss (IL) of insert, supra-aural and circumaural HPDs. Measurements spanned 1/3 octave bands from 125 Hz to 2 kHz. Attenuation was also measured via REAT procedures and finally the magnitude of the occlusion effect was examined via bone conduction audiometry. The ramifications of these data will be discussed in detail.