SYNOPSIS Total body potassium was measured in 103 healthy adults using a shadow-shield wholebody monitor of high sensitivity. The standard deviation from regression was smaller when total body potassium was correlated with height than with weight and was further reduced, to about 9 %, in a multiple regression using height and age. The advantages of this relationship over indices involving weight are discussed. The smallest standard deviation from regression, 7-5 %, was obtained when total body potassium was correlated with height, weight, and age. The usefulness of this relationship is discussed with comment on its limitations.A regression equation was derived between lean body mass (derived from height and weight) and total body potassium with a standard deviation from regression of 550% in males and 7.30% in females.

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The calibration procedure for the measurement of total body potassium with a high sensitivity shadow-shield whole-body counter is described. The sources of error have been analysed and it is shown that the estimated standard error for t'he procedure is 2.7y0 for a subject with 140 g of potassium, when 12K is administered to the subject as an internal standard. When a calibration factor is obtained from a derived regression equation relating this factor to the subject's weight and height, the estimated standard error is 3.9%. In sequential measurements in the same subject a change of body potassium equal to 4.6Ob would be significant.

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