To study the effects of steroids on the pulmonary lesions in experimental hypersensitivity pneumonitis, rabbits were sensitized to ovalbumin (OA) by injections of OA into footpads and 3 weeks later they were subjected to two successive aerosol challenges with OA at an interval of 48 hr. Injections of hydrocortisone sodium succinate 10 mg twice daily (but not at the reduced dosage of 5 mg twice daily) or methylprednisolone acetate 5 mg twice daily beginning 30 min before the first challenge and continued to the time of killing reduced the extent and intensity of vasculitis in both the treated groups and showed less alveolar septal thickening in the hydrocortisone treated group and less alveolar consolidation in the methylprednisolone treated group compared to the pulmonary lesions in the rabbits which were sensitized and then subjected to OA aerosol challenges, but received no treatment.

In view of the observation that even in a steroid sensitive species like the rabbit, extensive pulmonary changes like alveolar consolidation, septal thickening and vasculitis persisted in spite of treatment with relatively large doses of these steroids, it was felt that in human hypersensitivity pneumonitis steroids might only suppress the warning symptoms without substantially affecting the progress of the pulmonary lesions.