The aim of this study was to assess the relationship between changes in plasma catecholamine concentrations and intraarterial blood pressure (BP) measured simultaneously during resection of phaeochromocytoma (n = 14). Arterial plasma concentrations of noradrenaline (NA), adrenaline (A) and dopamine (DA) were measured by a radio-enzymatic method. Arterial NA concentrations (pmol/ml; median and Wilcoxon 95% CI) were 71.8 (46,162) before induction of anaesthesia, 113.0 (79,231) after intubation, 375.0 (285,931) during tumour handling and 32.5 (18,88) following tumour removal. Simultaneous mean BP values (mmHg; Mean ± SEM) were 119 ± 8, 114 ± 7, 159 ± 7 (p = 0.0001) and 72 ± 6 (p < 0.0001) respectively. At the time of tumour handling there was a weak correlation between plasma NA and A combined and mean BP (r = 0.583,p = 0.029) and a stronger correlation between log plasma NA and A combined and pulse pressure (r = 0.749,p = 0.008). The very large rises in plasma catecholamine concentrations and in BP are likely to have been causally related. Individual patients maintained a constant ratio of NA to A in plasma from pre-induction to tumour handling (r = 0.916,p < 0.0001). The maintenance of a constant NA: A ratio suggests that the pattern of catecholamine synthesis and release may be a characteristic of the individual tumour.