we examined the light microscopic changes in the lungs of rabbits exposed to grain dust for variable periods of time , to determine whether an animal model of grain worker 's lung could be developed . 
 experimental animals were exposed to grain dust at a concentration of 20 mg / m3 for 7 hr / day , 5 days / week , for up to 6 months . 
 the lungs of these rabbits demonstrated a granulomatous interstitial pneumonitis associated with exudation of mononuclear cells into the alveoli and conducting airways . 
 these changes appeared within 5 days of the onset of exposure and reached a peak at 3 weeks but were sustained through the longest exposure interval . 
 no abnormalities were observed in the lungs of control rabbits . 
 these results show three points of consistency with those obtained in epidemiologic studies of grain elevator workers . 
 first , the rapid appearance of the experimental changes suggests that the mechanism of tissue injury may not be immunologic . 
 second , the occurrence of the histopathologic alterations in the interstitium , alveoli , and airways corresponds with the combined restrictive and obstructive ventilatory defect described in the human epidemiologic studies . 
 third , the absence of lung fibrosis in rabbits exposed to dust for 6 months suggests that the pneumonitis is reversible . 
 thus this experimental model shows promise of helping to clarify the nature and mechanism of the adverse pulmonary effects of grain dust.imagesfigure 1.figure 2 .