Urethane-anesthetized rats were bled to otherwise irreversible haemorrhagic shock (mean arterial pressure = 18-25 mmHg) and then i.v. treated with ACTH-(1-24) (160 micrograms/kg) or saline. In comparison with sham-operated, non-shocked controls, bled rats showed a significant reduction in Bmax for [3H]Dihydroalprenolol and [3H]Dihydroergocryptine in heart ventricles, and for [3H]Yohimbine in spleen capsule. Neither the Kd of heart and spleen adrenoceptors nor the Bmax or Kd of brain adrenoceptors were affected. Treatment with ACTH-(1-24) restored to normal the Bmax for [3H]Dihydroalprenolol in heart ventricles, and for [3H]Yohimbine in the spleen capsule. These data indicate that the anti-shock effect of ACTH-(1-24) in bled rats is associated with a restoration of heart and spleen responsiveness to adrenergic stimuli.