The renin-angiotensin-aldosterone system plays a key role in the regulation of fluid and electrolyte balance. Angiotensin-converting enzyme inhibitors inhibit angiotensin-converting enzyme and have been shown to be effective in many cardiovascular diseases. They should be considered for the treatment of hypertension in patients with heart failure, previous myocardial infarction, diabetes, or proteinuria. There are a number of side-effects associated with angiotensin-converting enzyme inhibitors, especially persistent dry cough. Angiotensin II receptor antagonists (sartans) provide a more specific blockade of the renin-angiotensin-aldosterone system and are associated with fewer side-effects, including cough. Their long-term efficacy and tolerability in the treatment of patients with hypertension has, however, yet to be established. Periodic monitoring of renal function and electrolytes is required in patients treated with an angiotensin-converting enzyme inhibitor or a sartan.