The purpose of this study was to determine the value of calcium pidolate in the treatment of involutional osteoporosis. This compound has been reported to be better absorbed than other calcium salts, to lower the levels of parathyroid hormone (PTH) and to raise those of growth hormone (GH). We accordingly treated one group of 10 women suffering from involutional osteoporosis with the equivalent of 1 g elemental calcium and administered a placebo to a second group of 10 osteoporotic women whose mean age and body surface area were comparable. Basal sequential multiple analysis (SMA-12) was performed in all subjects to determine calcium, phosphorus, alkaline phosphatase (ALP) and total protein levels, the same blood samples being used for the evaluation of mean PTH, GH and osteocalcin (BGP). Urinary 24-h calcium excretion was determined and the calcium/creatinine (Ca/Cr) and hydroxyproline/Cr (HP/Cr) ratios were measured in 12-h fasting urine samples, the results being corrected for glomerular filtrate. The same parameters were measured again following a month of uninterrupted treatment. After 30 days, we observed no differences in either group as regards calcaemia, phosphataemia, ALP, total proteins, PTH, GH, BGP or 24-hour calciuria. The only noteworthy changes seen were significant decreases (P less than 0.001) in the Ca/Cr and HP/Cr ratios in the group treated with calcium pidolate. These results show that calcium pidolate at the dose administered inhibits bone resorption but does not affect the levels of PTH, GH, BGP or ALP in the medium term. Our findings indicate that it has no influence on bone formation.