Synthetic flocked fabric made from nylon, rayon or polyester is used in many industrial applications. A number of sporadic illnesses have been reported in the flocking industry during the last decade. Symptoms included interstitial pneumonitis, changes in pulmonary function, lymphocytic infiltration and mild fibrosis. Health Hazard Evaluations conducted by the National Institute for Occupational Safety and Health (NIOSH) failed to identify a specific set of symptoms or an explicit etiologic agent. However, when the affected workers were isolated from workplace exposure, their symptoms diminished. In contrast, if occupational exposure continued, the symptoms worsened. In view of these insights, and because the specific etiology of this disease remained unidentified, NIOSH organized a review in January 1998 of all the lung biopsies available from cases with work histories in the flocking industry. From a total number of 20 cases, 15 biopsies were reviewed by six pathologists to assess the type, severity and pattern of pulmonary inflammation, pulmonary lesions, fibrosis and other changes. These histopathological studies revealed a characteristic peribroncholitis lesion associated with lymphoid hyperplasia and abrogates. The pattern and transient nature of this distinctive lesion was suggestive of the toxicologic and immunologic nature of the etiologic agent. To evaluate the characteristic inflammatory response, we conducted short term in vivo studies in rats intratracheally exposed to a single dose of nylon dust, washed airborne dust and soluble fraction of the dust. Significant findings of these histopathological studies and toxicologic studies are presented here.