The brainstem auditory evoked response (BAER) is an auditory evoked potential that can be recorded non-invasively from the scalp, in both human and non-human subjects. The human BAER is a series five to seven vertex-positive peaks that occur within 10 ms from click-stimulus onset. These peaks are commonly labelled with capital Roman numerals. In humans, wave I appears to represent activity of the acoustic portion of the eighth nerve, wave III represents activity of the caudal brainstem and wave V represents activity of more rostral brainstem centers. The BAER peak amplitudes are typically less than 1 microvolt in humans, and are much smaller than the background electrical activity. Therefore, to extract these small potentials, time-domain signal averaging is required. Several thousand stimulus presentations are typically needed for the signal-to-noise ratio to reach acceptable levels. The BAER is not strongly dependent on subject attention or level of arousal. However, it varies systematically with normative subject factors such as age, gender and temperature. Similarly, it varies in predictable ways with hearing loss and is influenced by lesions of the acoustic portion of the eighth nerve and the tracts and nuclei of the auditory brainstem. It is also strongly dependent on stimulus parameters. The latencies of the various peaks increase and peak amplitudes decrease with increasing stimulus rate and decreasing stimulus level. The above-described features of the BAER have led to its popularity as both a clinical and a research tool. The reader interested in an overview of the BAER should refer to a general textbook on this topic [1,2]. This review assumes a basic understanding of the BAER, including its stimulus dependencies. This paper will review work by Burkard and colleagues concerning the effects of continuous, broadband masking noise on the click-evoked BAER.