On November 7, 2001, the National Institute for Occupational Safety and Health (NIOSH) received a request for a health hazard evaluation (HHE) from Department of Health and Human Services (DHHS) representatives regarding indoor environmental quality (IEQ) problems at the Federal Office Building, 26 Federal Plaza, New York City (NYC), New York. This building is located approximately 5 blocks northeast of the World Trade Center (WTC) disaster site. DHHS employees in the building expressed concerns regarding potential exposures and health effects related to the attacks on, and subsequent collapse of, the WTC. Because of the immense impact the WTC attack had on the lives of NYC residents and workers, as well as the concerns of many employees about ongoing security issues, NIOSH investigators included an assessment of mental health symptoms in the HHE. On November 12-15, 2001, NIOSH investigators conducted a site visit at the Federal Office Building to perform an environmental survey and meet with employees. A second site visit for a questionnaire survey was performed on December 4-5, 2001, and a similar questionnaire survey among a comparison group of DHHS employees in Dallas, Texas, was performed on December 12, 2001. Area air samples in the Federal Office Building were collected to measure concentrations of elements, asbestos, volatile organic compounds (VOCs), total dust, polynuclear aromatic hydrocarbons (PAHs), and polychlorinated biphenyls (PCBs). Bulk samples of settled material were collected at the 44th floor air intake and analyzed for elements and asbestos. Qualitative wipe samples of dust on surfaces were collected in various work areas and analyzed for elements. Carbon monoxide was monitored at various locations, including areas where employees had noted potential health problems, the 44th floor air intake, and near the basement loading dock. Additionally, on approximately every 5th floor, carbon dioxide (CO2), small particle counts, temperature, and relative humidity measurements were collected. One of the bulk samples of settled material indicated the presence of chrysotile asbestos (in the range of 1 - <3 percent). No asbestos fibers were found in the air. Many of the air samples collected inside the building indicated that concentrations of contaminants were below the limit of detection (LOD) for the method used. The concentrations of volatile organic compounds we found in our sampling were similar to concentrations we have found in other offices (outside NYC and unrelated to the WTC disaster) evaluated by NIOSH. One hundred ninety-one (68 percent of the 279 available) NYC Federal Office Building employees completed the questionnaire; 155 (47 percent of the available 328) Dallas DHHS employees completed the questionnaire. A variety of constitutional symptoms, most related to headache, eye, nose, and throat irritation, and irritation of the respiratory tract, were reported more frequently among the workers in NYC compared to those in Dallas. The most commonly reported symptoms among workers in NYC were eye and nose/throat irritation - both were reported by more than 60 percent of participants, compared to 12 (prevalence ratio [PR] 5.0, 95 percent confidence interval [95 percent CI] 3.2 - 7.7) and 21 percent (PR 3.1, 95 percent CI 2.3 - 4.3) (respectively) in Dallas. Measures of medical care for these constitutional symptoms did not differ between the workers in NYC and Dallas. Workers in NYC were more likely than those in Dallas to experience both depressive (prevalence ratio [PR] 3.4, 95 percent confidence interval [CI] [1.9 - 5.9]) and post traumatic stress disorder (PTSD) (PR 5.7, 95 percent CI [2.5 - 13.1]) symptoms. The prevalence of symptoms varied by agency within DHHS. Because our HHE was performed more than two months after the WTC disaster, we are unable to document occupational exposures of Federal Office Building employees closer to the time of the WTC disaster. No exploration of an association between exposure to potential air contaminants present at the time of our HHE and reported symptoms was possible because measured concentrations of air contaminants were too low. We observed that constitutional symptoms (such as headache, eye, nose, and throat irritation, and symptoms affecting the respiratory tract) were more prevalent among NYC Federal Office Building employees than the employees in Dallas. Symptoms associated with depression and stress were also more commonly reported among workers in NYC; the prevalence of both constitutional and mental health symptoms varied by agency within DHHS. Our survey revealed no occupational exposures to substances at concentrations which would explain the reported symptoms; however, we are unable to assess potential occupational exposures of Federal Office Building employees in the time immediately after the WTC disaster. Although our data suggest that an increase in social support might be associated with fewer reported symptoms of depression and stress, an evaluation of all factors which may be related to the reported symptoms was not performed in this HHE. Recommendations are provided in the report to assist DHHS management in addressing these findings.