Hypertension is a leading risk factor for cardiovascular disease. We previously found that 14% of people with hypertension have primary aldosteronism (PA), characterised by autonomous aldosterone secretion from the adrenal gland(s). PA is associated with a higher risk of cardiovascular complications compared to sex, age and blood pressure-matched essential hypertension. Targeted treatment with either unilateral adrenalectomy or mineralocorticoid receptor (MR) antagonists can mitigate many of these adverse cardiovascular consequences, although these treatments are not always tolerated or fully effective at lowering blood pressure, highlighting the need for novel approaches for the management of hypertension in PA. The gastrointestinal microbiota is an increasingly recognised factor influencing many health and disease states including hypertension. The MR is highly expressed in the gastrointestinal tract where it regulates the expression of the epithelial sodium channel, and aldosterone activation of the macrophage MR impacts the innate immune system which plays an important role in the gastrointestinal system. However, the role of the gastrointestinal microbiota in PA and treatment response has never been studied. We hypothesise that the analysis of the gastrointestinal microbiota in patients with PA, before and after targeted treatment, will provide unique insight into the effect of aldosterone on gastrointestinal microbiota, how it may influence blood pressure and the response to treatment in patients with aldosterone-mediated hypertension.