1. Two patients with adrenaline-only secreting phaeochromocytomas and primary aldosteronism were studied. 2. Urinary adrenaline levels were raised and plasma adrenaline was not suppressed normally following administration of clonidine. Plasma aldosterone to plasma renin activity ratios were repeatedly elevated. 3. Both had large intra-adrenal phaeochromocytomas visible on computerized tomography (CT) scanning. Surrounding adrenal cortical tissue contained an adenoma in one and nodular hyperplasia in the other. 4. Following removal of the adrenal gland containing the phaeochromocytoma, plasma and urinary adrenaline levels, and plasma aldosterone to plasma renin activity ratios returned to normal. 5. Adrenaline-only secreting phaeochromocytomas and primary aldosteronism have been rarely diagnosed even as separate entities, but reliable screening tests are now available. 6. Simultaneous presence of these two conditions of hormone excess is probably a chance occurrence. Alternatively, there may be a genetic predisposition to endocrine dysplasia, or an interaction between the contiguous medullary and cortical tissues, particularly after the normal architecture has been disturbed by an enlarging phaeochromocytoma.