A recombinant human parathyroid hormone, rhPTH-(1–84), which is currently in Phase II clinical trial, and hPTH-(1–31)NH2 (Ostabolin) are promising anabolic agents for treating osteoporosis because they can stimulate cortical and trabecular bone growth in osteopenic, ovariec-tomized (OVX) rats and in osteoporotic, postmenopausal women when injected subcutaneously and intermittently at low doses. We have now found that, despite their different sizes and signaling properties (rhPTH-(1–84) stimulates adenylyl cyclase and phospholipase C; hPTH-(1–31)NH2 only stimulates adenylyl cyclase), they are equally osteogenic in OVX rats. Thus daily subcutaneous injections of 0.6 nmol/ 100 g of body weight of rhPTH-(1–84) or hPTH-(1–31)NH2 into 3-month-old OVX rats for 6 weeks starting 2 weeks after OVX equally reduced the otherwise large OVX-triggered loss of femoral trabecular bone. Daily subcutaneous injections of 0.4 or 0.8 nmol/100 g of body weight of the two agents for 6 weeks also equally increased the mean thickness of the remaining femoral trabeculae in 3-month-old and 1-year-old OVX rats to 20 to 80% above the value in normal animals when started 9 weeks after ovariectomy.