A low level inhalation study was conducted with carefully characterized fibrous-glass (14808607) to assess the adequacy of the OSHA standard and the NIOSH recommended standard of 5mg/m3 as total dust and to characterize the pulmonary responses from a physiological and pathological approach. Five experimental groups were developed using 60 young male Cynomolgus-monkeys and 500 Fischer-344-rats. Animals were exposed for 7 hours a day, 5 days a week, for period of 72 weeks or 86 weeks. Commercial grade glass fibers were used. Exposure conditions were as follows: A, greater than 3.5 micrometers diameter and greater than 20 micrometers long with a mass of 15mg/m3 with binder; B, less than 3.5 micrometers diameter and greater than 10 micrometers long, mass 15mg/m3, with binder; C, less than 3.5 micrometers diameter, longer than 10 micrometers, mass of 5mg/m3, without binder; D, less than 3.5 micrometers diameter, less than 10 micrometers long, mass 5mg/m3, without binder; E, filtered and conditioned air. Significantly reduced expiratory reserve volumes were demonstrated at 18 months in both 15mg/m3 groups, with a suggested trend toward increased inspiratory capacities. The only unequivocal effect of the fibrous- glass inhalation was macrophage aggregates with phagocytized fibrous- glass in the lungs and tracheobronchial lymph nodes. Grossly visible plaque like foci resulted from accumulations of granulomatous foci in pleural and subpleural locations. The more severe responses were found in rats under treatment-D. The severity of the response in monkeys was similar for all groups except for treatment-A which did, however, have monkeys with mildly increased numbers of lymphoid nodules or aggregates in peribronchiolar and perivascular areas. Mononuclear cell leukemia was statistically elevated when each fiber exposed group was individually compared with the control group.