To investigate the effects of unilateral adrenalectomy on the postoperative course and laboratory parameters, 40 patients with a renal tumour were randomized either to undergo (n = 20) or not to undergo (n = 20) ipsilateral adrenalectomy. Adrenal hormone (cortisol, epinephrine, norepinephrine and aldosterone), adrenocorticotropic hormone, electrolyte, creatinine, growth hormone, glucose, insulin and free fatty acid concentrations were measured preoperatively and postoperatively. Cortisol and epinephrine concentrations were elevated immediately after the operation but returned to preoperative levels within the first 2 postoperative days. There were no significant differences between the adrenalectomy and non-adrenalectomy groups, except that the cortisol concentration was higher in the latter in the afternoon of the day of surgery. The conclusion is that no long-term shortage of adrenal hormones is caused by unilateral adrenalectomy. Other metabolic and endocrine responses were identical in the groups. Thus ipsilateral adrenalectomy does not seem to be harmful to the patient and the need for it must be resolved on the basis of local tumour factors.