The relationship between plasma leptin and catecholamine concentrations during chronic and acute catecholamine excess is studied. Patients with phaeochromocytoma, divided according to gender, were examined under basal conditions (n = 18) and at selected time-points during surgical removal of the tumour (n = 12). Appropriate controls were used (n = 23) for the basal study. Plasma leptin was determined by radioimmunoassay (RIA) and plasma noradrenaline (NA) and adrenaline (A) by high-performance liquid chromatography (HPLC). Statistical evaluation employed Student's t-test, Wicoxon test and Spearman's correlation coefficient. Gender-related differences in plasma leptin in normal subjects was confirmed, and these were maintained in the patients. Phaeochromocytoma patients had normal plasma leptin levels in the basal state and decreased levels following the massive catecholamine surge provoked by surgery. Plasma leptin concentration did not correlate with plasma NA or A in either group studied. In the patients with phaeochromocytoma, acute but not chronic catecholamine excess affected plasma leptin, suggesting a role for sympathetic activity in modulating leptin release.