1. in twenty normal subjects and five patients with disturbances of potassium balance, the potassium concentration in leucocytes was measured by a modified technique.
2. The precision of the method was three to four times greater than that of techniques previously described, with a coefficient of variation for duplicate analyses of 2.3%.
3. A comparison between intraleucocyte potassium concentration and total body potassium in five patients with pathological alterations in their potassium balance showed that intracellular potassium concentration may reflect the clinical state better than total body potassium.