Extreme overexposure to ammonia can cause irreversible pulmonary damage. There, however, is no credible evidence that inhaling a small amount of ammonia leads to chronic lung impairment. In the recent past, ammonia has been the focus of several regulatory agencies' activities. The OSHA (Occupational Safety and Health Administration)changed its workplace exposure limit to a 35 ppm (part per million) STEL (short term exposure limit). The ACGIH (American Conference of Governmental Industrial Hygienists) set a TLV (threshold limit value) for ammonia at 25 ppm as a TWA (time-weighted average). Many States have or are in the process of setting an AAC (acceptable ambient concentrations) for ammonia. Ammonia is currently on the SARA 313 list (Superfund Amendments and Reauthorization Act), prompting the ATSDR (Agency for Toxic Substance and Disease Registry) to prepare a toxicological profile for ammonia. The DOT (Department of Transportation) revoked its proposal to reclassify anhydrous ammonia as a poison, and retained the non-flammable gas classification and required an inhalation hazard warning on domestic shipments. Finally, the EPA (Environmental Protection Agency) is currently attempting to set an RfD (risk reference dose.- defined as an estimate of the daily exposure to the human population that likely is to be without an appreciable risk of deleterious effect during a lifetime) for ammonia. Each of these areas of regulation has a profound impact on several industries. It is extremely important that any standards set act to both protect human health and retain the necessary production of ammonia. The purpose of this report is to present an overview of the health effects of ammonia. The focus is on the effects following inhalation UNOCAL Corporation, Los Angeles, California.