This study was conducted using immunohistochemistry to detect the expression of the prooncogen c-fos in the corticoadrenal of the rat with renal hypertension. A model of renal hypertension was established through narrowing a renal artery of the rat. An antiserum against FOS oncoprotein was used to immunohistochemically detect the activated cells of the corticoadrenal. In the experimental group, C-FOS-immunoreactive (ir) nuclei proved to be present in the zona glomerulosa. Few labeled nuclei were seen in the lateral part of the zona fasciculata. An increasing number of C-FOS-ir nuclei was demonstrated in the intermediate part of the zona fasciculata. The highest concentration of the labeled nuclei was found in the inner part of the zona fasciculata. Scattered FOS-ir nuclei existed in the zona reticularis. The labeled nuclei were often round or oval in shape, and different in size. Only were a few labeled nuclei seen in the sham-operated group and no FOS-ir nuclei in normal control group. The result suggested that all three zones of the corticoadreal were modified subsequent to induction of renal hypertension.