Plasma glucose, osmolality and insulin have been investigated during hemorrhage in non-starved rats. The rate of blood loss leading to hemorrhages of 44% and 55% of the estimated original blood volume determined the patterns of response. Substantial hyperglycemic hyperosmolality and insulin values appropriate for the raised levels of glucose were observed in the animals bleeding more rapidly. The slower rate of hemorrhage was associated with only moderate hyperglycemia and hyperosmolality, while the insulin values rose to very high levels, 45 times basal. It is postulated that altered glucose-insulin metabolism in haemorrhage may have important consequences for fluid homeostasis, and the rate of bleeding is the fundamental factor steering this effect.