Spironolacotone and eplerenone are mineralocorticoid-blocking agents. These compounds block both the epithelial and non-epithelial actions of aldosterone with the latter assuming increasing clinical importance. Spironolactone and eplerenone both effectively reduce blood pressure either as mono- or add-on therapy; moreover, they each offer survival benefits in diverse circumstances of heart failure and the potential for renal protection in proteinuric chronic kidney disease. However, as the use of mineralocorticoid-blocking agents has increased the hazards inherent to use of such drugs has become more apparent. Whereas; the endocrine side-effects of spironolactone are in most cases little more than a cosmetic annoyance the potassium-sparing effects of both spironolactone and eplerenone can prove fatal if sufficient degrees of hyperkalemia develop. However, for most patients the risk of developing hyperkalemia in and of itself should not discourage the sensible clinician from bringing these compounds into play. Hyperkalemia should always be considered as a possibility in any patient receiving one or the other of these medications. As such, steps should be taken to lessen the likelihood of its occurring if therapy is being contemplated with agents in this class.