Routine renal tubular investigations in 8 osteoporotic men, in whom phosphorus/calcium balance studies were normal or almost normal revealed moderate phosphorus (PD) or bicarbonate (BD) diabetes possibly responsible for their decalcification. Osteoporosis affected the spine and lower limbs, resulting in clinical pictures of frequently recurrent spontaneous algodystrophy. Histomorphometric studies revealed an increase in surface areas of resorption, the diagnosis of PD being based upon the finding at several successive investigations, in the absence of any drug treatment, of a phosphorus clearance of greater than 20 ml/min and/or a phosphorus reabsorption level of less than 80%. Arterial HC03 levels of greater than 21 mEg/l and a fractional bicarbonate excretion (FBE) of greater than 15% enabled the diagnosis of bicarbonate diabetes (proximal tubular acidosis). These cases of PD and BD appeared to be secondary to proximal tubulopathies for which no known etiology was found.