In a study of kidneys obtained from adult human subjects at necropsy, the specificity and sensitivity of the alizarin red S method for detecting calcification is confirmed.

A survey of the relevant literature indicates that, while calcification is frequently found in the human renal papilla at necropsy, conflicting opinions have been expressed regarding its anatomical site. In the present study of 62 adult human kidneys, in which specific renal disease had been excluded, papillary calcification was present in 43 (69 per cent). A detailed histological study of the papilla, using thin and thick sections, demonstrates the predominant site of calcification to be in the walls of the long loops of Henle, where it is closely related to the basement membrane.

The nature of papillary calcification and its possible relationship to the physiology of the renal medulla are briefly discussed. The question is raised as to the possible part played by the loops of Henle in the genesis of renal calculi.