Glucocorticoid therapy induced rapid involution of chronic granulomatous inflammation in rats by subcutaneous injection of carrageenin. Hydrocortisone acetate injected into the granuloma pouch at a dose of 3mg/kg/day for 3 days caused a marked involution of the granulomatous inflammation. After withdrawal of steroid treatments, however, rebound of the inflammation took place resulting in a rapid recovery not only in the wet weight and the dry weight of the granuloma but also in vascular permeability response and the volume of the exudate. Metabolic aspects of the rebound phenomenon suggested that the synthesis of some fractions of the granuloma proteins which involve proteins essential for DNA synthesis was activated before the reactivation of the synthesis of DNA and some other proteins. By repeated administrations at 12hr intervals with hydroxyurea (250mg/kg/day, into pouch) after the withdrawal of the steroid treatments, the rebound of the inflammation not only in proliferative phases but also in exudative phases was suppressed almost completely.