Naphthalene has been recently characterized as a likely human carcinogen by the U.S. Environmental Protection Agencys (EPA) Integrated Risk Information System (IRIS) Program in a draft Toxicological Review of Naphthalene (U.S. EPA, 2000), based on new information from a two-year inhalation rat bioassay conducted by the National Toxicology Program (NTP, 2000). In the NTP study, positive trend increases in the incidences of two rare nasal tumors, olfactory neuroblastomas in males and females and adenomas of the respiratory epithelium in males, were observed. EPA derived an inhalation unit risk was derived from these findings. The draft assessment was reviewed by an independent external peer review panel in July 2004. Among comments made by the external peer review panel was the desirability of future research to characterize naphthalenes carcinogenic mode of action. To further discuss this comment, EPA decided to sponsor a one-day peer consultation workshop, inviting experts in naphthalene toxicology and chemistry, inhalation toxicology, genetic toxicology, and risk assessment to discuss the specific types of studies that would improve characterization of the mode of action of nasal tumor formation and provide estimates of required research time and resources. The expert opinions and recommendations from this workshop will be considered by EPA in determining a course of action for the development of a scientifically defensible human risk assessment for naphthalene inhalation carcinogenicity.