The more potent "loop" diuretics are being used with increasing frequency. The elderly constitute a growing portion of the population undergoing treatment with diuretics. The alterations in renal function and pharmacokinetics in the elderly (over 60 years of age) may result in the development of certain adverse effects. In patients over 70 years old, there is a progressive decline in overall renal function, resulting in a more than 50% decrease in glomerular filtration rate. Most of the pharmacokinetic changes in the elderly consist of alterations resulting in enhanced plasma levels of any given drug; diminished hepatic drug extraction, detoxification/metabolism or prodrug conversion; decreased renal excretion of drug; and diminished volume of distribution of drug. Adverse reactions to diuretics may be grouped into metabolic changes (e.g., hypokalemia), physiologic alteration (e.g., volume contraction), toxic manifestation (e.g., interstitial nephritis) and allergic or idiosyncratic phenomena (e.g., rash or thrombocytopenia). There is general agreement that significant hypokalemia, particularly among elderly patients receiving digitalis glycosides, is significant and requires therapy. Diuretic-associated hypokalemia reflects the potency and duration of action of a diuretic, factors modulating potassium balance including dietary intake and concurrent medical processes. The short duration of action and greater natriuresis relative to kaliuresis characteristic of loop diuretics may result in a lesser degree of hypokalemia than that seen with traditional thiazide diuretics.