Sixteen Yorkshire swine weighing 15-20 kg were studied to compare the effects of suxamethonium, atracurium and vecuronium on intracranial pressure (ICP), heart rate (HR), arterial blood pressure (BP), and cerebral perfusion pressure (CPP) in swine with normal or elevated ICP. In each animal an intracranial pressure-volume curve was produced by the inflation of an epidural balloon. The baseline ICP (Po), the ICP at the inflection point (Pi) and on the steep portion (Pmax) of the pressure-volume curve were identified and the balloon volumes recorded. The animals were assigned to receive either suxamethonium 1.0 mg/kg, atracurium 0.6 mg/kg, vecuronium 0.2 mg/kg, or saline placebo intravenously at three conditions: First, with the epidural balloon deflated Po, next at Pi, then at Pmax. Neither atracurium, vecuronium, nor placebo produced any statistically significant effect on HR, BP, ICP, or CPP at any baseline level of ICP. Suxamethonium produced an early fall in ICP (0.8 +/- 0.3, 2.6 +/- 1.0 and 3.5 +/- 1.3 mmHg at Po, Pi and Pmax respectively: P = .0005) followed by a rapid rise above the pre-infusion level (1.8 +/- 0.6, 2.8 +/- 0.6 mmHg, and 2.2 +/- 0.5 mmHg at Po, Pi and Pmax respectively: P = .0005). A fall in BP coupled with the rise in ICP resulted in a fall in CPP (5.8 +/- 2.3, 6.1 +/- 1.2, and 6.3 +/- 1.8 mmHg at Po, Pi and Pmax respectively: P = .0005). Although the fall in CPP was not large, in the presence of elevated ICP, where CPP already is marginal, such a decrease may compromise cerebral blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)