The acute toxicity of budesonide is low and of the same order of magnitude and type as that of the reference glucocorticoids studied (beclomethasone dipropionate, flucinolone acetonide). Results from subacute and chronic toxicity studies show that the systemic effects of budesonide are less severe than or similar to those observed after administration of the other glucocorticosteroids . decreased body weight gain and atrophy of lymphoid tissues and adrenal cortex. An increased incidence of brain gliomas in male rats in a carcinogenicity study could not be verified in a repeat study, in which the incidence of gliomas did not differ between any of the groups on active treatment (budesonide, prednisolone, triamcinolone acetonide) and the control groups. Liver changes (primary hepatocellular neoplasms) found in male rats in the original carcinogenicity study were noted again in the repeat study with budesonide, as well as with the reference glucocorticosteroids. These effects are most probably related to a receptor effect and thus represent a class effect.