ABSTRACT
This study divided 30 adult male albino rats into five groups: Group I [n =10] served as control, groups II and III [n = 5/each group] were exposed to 30ppm of HCHO vapor during six hours/day, five days/week for successive four andeight weeks, respectively, and Groups IV and V [n = 5/each group] were leftunder similar experimental conditions without any exposure for the same time-interval after being exposed to the above mentioned concentration andduration. Histological, histochemical and ultrastructural studies were alldone on lung tissue using both light as well as electron microscopes. Manymorphological alterations were observed in the lung tissue of rats exposed toformaldehyde spray. These changes were more evident with the electronmicroscopic examination and more apparent in animals exposed for prolongedperiods of time. In addition, many of these changes were irreversible aftercessation of exposure to formaldehyde