The induction by endotoxin of Ca2(+)-independent nitric oxide (NO) synthase in the lung and liver of the rat was prevented by the glucocorticoids dexamethasone and cortisol but not by progesterone. The activity of the constitutive Ca2(+)-dependent NO synthase in the brain and the aorta was not affected by treatment with either endotoxin or glucocorticoids. In the aorta a Ca2(+)-independent NO synthase was also found following endotoxin treatment of rats, and this induction was likewise prevented by dexamethasone. The Ca2(+)-dependent NO synthase in the aorta was located in the vascular endothelium, whereas the Ca2(+)-independent enzyme was predominantly located in the vascular smooth muscle layer. Inhibition of induction of the Ca2(+)-independent NO synthase in vivo may underlie some of the physiological and pharmacological effects of the anti-inflammatory glucocorticoids.