Hypercalcemia is a serious and potentially lethal complication of many diseases. As a result, it is important to understand and to be familiar with the appropriate management of this condition which often is identified only accidentally. The approach to therapy must be tempered by an appreciation of the underlying disease state as well as by knowledge of whether or not emergency reduction of serum calcium is required. In the latter case, no firm rules based on serum calcium values can be applied. Rather, it is important to recognize that individual tolerance to hypercalcemia is variable and, furthermore, that it may reflect the rapidity with which the concentration of serum calcium increases. It is not uncommon, for example, to observe nearly asymptomatic patients with primary hyperpara thyroidism and a serum calcium of 15 mg/100 ml, yet to also see virtually moribund patients with rapidly progressive cancer and a serum calcium of 12 mg/100 ml. In these two extremes, of course, other factors such as debility and impaired renal function, may contribute to the clinical manifestations observed. In any case, one must use judgment of the patient's clinical status in assessing therapeutic needs. Associated conditions, such as renal impairment or cardiac arrhythmias, may alter the approach to be used.