Subtotally hepatectomized or sham-operated rats were bled to hypovolemic shock (mean arterial pressure = 18-25 mmHg) and then treated with an intravenous bolus injection of ACTH-(1-24), 160 ug/kg. The treatment caused a prompt and sustained reversal of hypotension, with survival of all sham-operated animals, at least for the first 2 h, while in hepatectomized rats the arterial pressure increase was negligible and there was a 50% mortality within 2 h after treatment. Moreover, the blood volume which could be drained from an arterial catheter prior to death, measured 15-20 min after ACTH injection, was 1.51 +/- 0.12 and 0.64 +/- 0.11 ml/100 g b.w. in sham-operated and hepatectomized rats, respectively. These results further support the idea that the effect of ACTH in haemorrhagic shock is due to the mobilization of blood pooled in peripheral reserve organs.