Rats with experimental streptozotocin-induced diabetes (75 mg/kg) were divided into two groups. One group was free fed (n = 8), the other group (n = 7) pair fed to a group of control animals (n = 8). The nitrogen and energy balances of the control rats were positive. In the free-fed diabetic rats the nitrogen balance was neutral and the energy balance higher than in controls. In the pair-fed diabetic rats the nitrogen balance was negative and the energy balance reduced. After 4 weeks the capacity of urea-nitrogen synthesis was: 8.1 +/- 0.6 mumol/(min 100 g body weight) (mean +/- SEM) in controls and 22.2 +/- 2.2 mumol/(min 100 g body weight) in both groups of diabetic rats. Initially, the whole body nitrogen content was 453 +/- 9 mmol. Four weeks later it was 536 +/- 19 mmol in controls, 410 +/- 21 mmol in the free-fed diabetic rats, and 315 +/- 6 mmol in the pair-fed diabetic rats. The largest changes occurred in the muscles, initially containing 278 +/- 6 mmol, 4 weeks later 328 +/- 8 mmol, compared to 234 +/- 19 in the free-fed diabetic rats and 166 +/- 18 mmol in the pair-fed diabetic rats. In conclusion uncontrolled diabetes is characterised by loss of nitrogen from muscles and most other organs. The losses from some organs are preventable by increased food intake. Irrespective of food intake the hepatic dynamics of amino nitrogen conversion is changed in a way that favours protein catabolism.