Male rats were exposed to noise for 6 running hours and the effects of pretreatment with the benzodiazepine diazepam on the adrenal gland were evaluated. Ultrastructural examination showed that, after noise exposure, zona reticularis cells resulted the more affected, exhibiting areas of diluted cytoplasm, disarranged endoplasmic reticulum, membrane vestigia and some altered mitochondria; diluted cytoplasmic areas appeared in noradrenaline-storing cells, too. On the contrary, zona reticularis cells from diazepam-pretreated and noise-exposed rats resulted significantly less altered, as well as the noradrenaline-storing cells. The present findings indicate that diazepam is able to exert some protective action on adrenal gland alterations due to noise exposure.