An apparent outbreak of mass psychogenic illness in an aluminum furniture assembly factory (SIC-2511) was described. A female employee working in the webbing department of a midwestern aluminum lawn furniture assembly factory became ill with symptoms of headache, nausea, dizziness, burning throat, and general weakness. She had complained of a strange odor before her illness. Within 1 hour 29 women had experienced similar symptoms and were taken to a local hospital and the factory was closed. Environmental monitoring found carbon-monoxide, carbon-dioxide (124389), and oxygen concentrations to be within acceptable limits. When the facility reopened several days later, 22 female employees including eight affected previously and five males became ill with similar symptoms. Environmental sampling again revealed no toxic agents. No additional mass outbreaks occurred; however, there were daily complaints of odors and and isolated occurrences of symptoms such as nausea and headache. A NIOSH investigation performed 60 days after the initial outbreak detected no toxic substances that could have caused the outbreak. A psychosocial questionnaire survey of 94 affected and nonaffected employees showed that workers who reported symptoms experienced more job dissatisfaction and stress, reported being bothered by noise and temperature variations, had generally poorer overall health, and had a higher prevalence of hysteria and hypochondria than nonaffected workers. The differences were statistically significant. The author concludes that the outbreak may have been caused by psychosocial factors since no environmental agents capable of causing the outbreak were found.