The effects of cerebral ischaemia by carotid artery occlusion and of a ganglionic blocking agent (Arfonad) on cardiac output and regional blood flows were studied after 15 min of haemorrhagic hypotension (mean arterial pressure 50 mmHg) in the rat. The microsphere technique was used for blood flow determinations. Animals subjected to haemorrhagic hypotension and simultaneous carotid artery occlusion (group BC) exhibited a stronger immediate vasoconstrictor response than animals subjected to haemorrhagic hypotension only (group B) and more blood had to be withdrawn to achieve stable hypotension at 50 mmHg (2.6 +/- 0.1 vs. 2.2 +/- 0.4 ml per 100 g body weight (body wt); P less than 0.05). However, group B showed the same decrease in cardiac output as group BC, but the blood flows of the kidneys, spleen, intestine, liver and skin were less deranged at the end of the hypotensive period. Groups B and BC exhibited similar intestinal ischaemic mucosal damage, measured as leakage of [125I]albumin. When induction of haemorrhagic hypotension was combined with ganglionic blockade administration (Arfonad) and carotid artery occlusion (group ABC), significantly less blood had to be withdrawn than in groups BC (1.6 +/- 0.2 vs. 2.6 +/- 0.1 ml per 100 g body wt; P less than 0.05). The blood flows of the kidneys, small intestine, liver, spleen and skin were less compromised in group ABC. In addition, group BC had more profound metabolic acidosis and were more haemoconcentrated than group ABC; moreover, group BC, tended to be hypoglycaemic and showed intestinal mucosal damage, whereas neither of these effects occurred in group ABC.(ABSTRACT TRUNCATED AT 250 WORDS)