The present study was performed to examine the effect of varying duration of noise exposure on rat adrenal gland. Animals were exposed to noise for 1, 6 and 12 h continuously and the sections obtained from exposed rats were compared to those from corresponding controls. No significant ultrastructural changes were found in the zona glomerulosa, while mitochondria of the zona fasciculata showed matrix dilution and cristolysis after 1 and 12 h of noise stress. At all exposure times examined, the zona reticularis exhibited areas of diluted cytoplasm, disarranged endoplasmic reticulum, membrane vestigia and some altered mitochondria. Diluted cytoplasmic areas appeared in noradrenaline- and adrenaline-storing cells after 6 and 12 h of exposure, respectively. Our findings indicate that each zona of the adrenal cortex and the two cell types of adrenal medulla show a differential reaction to noise stress.