Most people at one time or another have found themselves irritated or distracted by the background noise in a building. The irritation might have resulted in minor aggravation or may have been dramatic enough to hinder their work. This leads us to ask whether occupants are increasingly aggravated by noise the longer they are exposed to it, or if they naturally habituate to their acoustic environment. In an effort to answer this question, a study was completed in the "Indoor Environment Lab" at the University of Nebraska. This lab resembles a typical office and was specially constructed to be acoustically and thermally controlled. Subjects completed 38 total hours of testing in the lab over multiple days, during which time they were exposed to several background noise conditions over 20, 40, 80, and 240 minute trials. During the trials, subjects completed a variety of performance tasks and answered questions about their perception of the noise, the thermal environment and various other factors. End results aid in understanding the prolonged effects of typical heating, ventilating, and air-conditioning (HVAC) noise on worker productivity and annoyance. Copyright ASCE 2006.