This paper describes results on carcinogenesis in rats induced with diethylnitrosamine (DENA; 280 mg/kg single dose, i.p.). After inducing chemical carcinogenesis, the animals were treated with different compounds that affect cell proliferation and the effects on the blood prostaglandin E(2) (PGE(2)) levels were observed. These compounds were epidermal growth factor (EGF, 10 mu g/kg/24 h i.p., 7 days) and dexamethasone (4 mg/kg/24 h i.p., 7 days). The blood PGE(2) levels of rats were measured by RIA (Radioimmunoassay). The blood PGE(2) levels increased significantly following DENA and EGF administrations alone or together. Dexamethasone administration decreased the blood PGE(2) levels. In conclusion the data show that the increase in the plasma PGE(2) level by DENA treatment was enhanced by EGF but opposed by dexamethasone. This suggests that EGF may be effective as a promoter in chemical carcinogenesis.