Haemorrhagic hyperglycemia has been demonstrated to have beneficial effects on fluid homeostasis, and insulin resistance has been reported in vitro after haemorrhage. In the present study the interrelation of peripheral levels of insulin, glucagon, and adrenalin and the rate of glucose disappearance (Rd) in haemorrhagic hyperglycemia were determined in vivo. Rd was determined by single injection of 3-3H-glucose in three groups of postprandial rats: controls, rats submitted to rapid blood loss, and rats receiving a constant 30% glucose infusion. The level of hyperglycemia after bleeding was 22.9 +/- 1.9 mmol x 1(-1) (mean +/- 1 S.E.), and during infusion it was 20.4 +/- 1.4 mmol x 1(-1). The Rd value of controls was 8.2 +/- 0.5 mmol x 100 g-1 x min-1, during glucose infusion it was 34.1 +/- 0.6, and after haemorrhage it was 9.7 +/- 0.4. Both treatments increased insulin levels by greater than 200%. These results show an important role of insulin resistance in causing hyperglycemia after experimental haemorrhage in the rat.