The catecholamine and cardiovascular responses to intubation were investigated during halothane anaesthesia. Thirty patients were allocated randomly to two groups. Following induction of anaesthesia and muscle relaxation, group 1 was ventilated with 70% nitrous oxide in oxygen before intubation; group 2 received 1% halothane in addition. After intubation, both groups received 0.5% halothane. Arterial pressure and heart rate, and plasma noradrenaline and adrenaline concentrations were measured throughout the induction sequence. In group 1 intubation was associated with increases (from pre-induction values) in systolic arterial pressure of 13% and diastolic arterial pressure of 35%, although the plasma concentrations of noradrenaline did not alter significantly. In group 2, although there was a pressor response to intubation, no overall change in systolic arterial pressure and only a 13% increase in diastolic arterial pressure occurred when compared with pre-induction values. This response was associated with a 78% increase in the noradrenaline concentration; the adrenaline concentration did not alter significantly.