SummaryThe whole Body Counter of Liege University permits, by counting the naturally occurring ,40K isotope, the measurement of total body potassium (which can be practically considered as the intracellular potassium content) in human subjects. The accuracy of the measurements is 5 % for a counting time of 200 seconds. Normal values have been checked by the measurements of a great number of healthy individuals: regression equations have been computed according to age and weight. The fluctuations of normal values, when related to homogeneous groups, are rather small, and the meaning of pathological results seems unequivocal. The preliminary findings have confirmed an important decrease of body potassium in amyotrophy, cirrhosis of the liver, obesity and cardiac failure. A less pronounced, but statistically significant decrease was also found in equilibrated diabetes, essential hypertension and renal failure. Longitudinal studies have shown parallelism between the body potassium content and clinical evolution in patients with cirrhosis of the liver. The effect of haemodialysis on body potassium stores was also studied in patients with renal failure.