Cortisol is regenerated from cortisone by 11beta-hydroxysteroid dehydrogenase type 1 (11HSD1), amplifying glucocorticoid action in adipose tissue and liver. 11HSD1 inhibitors are being developed for type 2 diabetes and may be most effective in obesity, where adipose 11HSD1 is increased. However, the magnitude of regeneration of cortisol in different tissues in humans is unknown, hindering understanding of the pathophysiological and therapeutic importance of 11HSD1. In eight healthy men, we infused 9,11,12,12-(2)H4-cortisol and measured tracer enrichment in the hepatic vein as an indicator of total splanchnic cortisol generation. Oral cortisone (25 mg) was then given to measure first-pass hepatic cortisol generation. In steady state, splanchnic cortisol production was 45 +/- 11 nmol/min when arterialized plasma cortisone concentration was 92 +/- 7 nmol/l. Extrapolation from hepatic cortisol generation after oral cortisone suggested that, at steady state, the liver contributes 15.2 nmol/min and extrahepatic splanchnic tissue contributes 29.8 nmol/min to the total splanchnic cortisol production. We conclude that tissues draining into the portal vein, including visceral adipose tissue, contribute substantially to the regeneration of cortisol. Thus, in addition to free fatty acids and adipokines, the portal vein delivers cortisol to the liver, and inhibition of 11HSD1 in visceral adipose tissue may indeed be valuable in ameliorating insulin resistance in obesity.