A double-blind study was performed to test the metabolic effects of tricalcium phosphate (TP) and calcium carbonate (CC) on serum calcium (SCa), serum phosphorus (SP), and immunoreactive intact serum parathyroid hormone (SPTH) levels in two groups of 24 subjects. The mean age of young subjects was 29.5 years, and elderly subjects, 65.9 years. These subjects fasted overnight for 12 hours, but with good hydration, before the tests. Following a 2-hour baseline-urine collection, 1200 mg elemental calcium (as CC or TP in tablet form) was chewed and ingested and 2-hour postload urines were collected. Blood was drawn immediately before and at 1, 2, and 4 hours after calcium load. The results showed that SCa and SP increased, whereas SPTH decreased with both preparations. The increment of SCa was similar after oral load of either calcium salt in both groups. The increment of SP after TP load was more than after CC. The urinary calcium/creatinine ratio (UCa/Cr) increased significantly after both preparations in the young group. The urinary phosphorus/creatinine ratio (UP/Cr) did not change significantly following TP, but decreased significantly after CC load in the young subjects. However, in the elderly individuals, the UP/Cr increased after TP load but did not change following CC, with statistical significance. The difference of urinary cyclic adenosine monophosphate/creatinine ratio (UcAMP/Cr) was not significant in both groups with either preparation. In summary, there was a similar rise in SCa and an equivalent fall in SPTH between TP and CC, in both young and elderly individuals.