1. Administration of dexamethasone, 8 mg/day (0·02 mmol/day), for 5 days to normal subjects produced negative nitrogen balance, due to early and sustained increases in urinary urea nitrogen excretion.
2. In eight subjects ingesting 0·9–1·6 g of protein day−1 kg−1 body weight the cumulative increment in urea nitrogen excretion averaged + 12·5 g (sem 2·8, P < 0·01) over the 5 days of glucocorticoid administration.
3. Increases in urinary urea nitrogen excretion could be related to both plasma alanine and blood glutamine changes by using a multiple regression equation.
4. These results suggest that corticosteroids induce increased release of alanine and glutamine by peripheral tissues, which may augment urea formation and negative nitrogen balance.
5. The correlation between increments in urea nitrogen excretion and increases in plasma arginine remains unexplained.