Corticosterone both inhibits cell proliferation in the liver of adult rats and synchronizes division of liver cells after partial hepatectomy. By adrenalectomy, corticosterone can be eliminated from the circulation at least for certain time. Additionally it can be inactivated in the liver cell by competitive inhibition of its cytoplasmatic receptor. Both these procedures lead to an increased cellular proliferation. The influence of these processes on the development of chemically induced liver tumors has been investigated. Animals died significantly earlier from hepatomas, when they had been treated with both diethylnitrosamine and steroids belonging to the group of gestagens, androgens and estrogens (which stimulate proliferation). Therefore, a tumor-promoting effect of these substances can be assumed.