SUMMARY Absorption of calcium from the gastro‐intestinal tract was studied by a new and simple method, combining the use of Ca47, a gamma‐emitting isotope of calcium, and a whole‐body counter. The physical characteristics of the isotope and the design and efficiency of the whole‐body counter are described. The results of 86 studies carried out on 53 subjects with normal or disturbed calcium metabolism are presented. Absorption of Ca47 as estimated by whole‐body counting correlated well with the clinical state and experimental condition. The advantages and disadvantages of the technique are briefly discussed.