The use of angiotensin converting enzyme inhibitors in combination with other antihypertensive agents. Angiotensin converting enzyme (ACE) inhibitors have additive effects with most other antihypertensive agents, but the mechanisms of these interactions vary. With diuretics the interaction with ACE inhibitors can be explained by their contrasting effects on the renin-angiotensin system, while with calcium antagonists it may be attributed to independent mechanisms of action. With beta-blockers there is a variable additive effect, which has been proposed to be due to more complete blockade of the renin-angiotensin system than can be obtained with either type of agent alone. 