Effects of h-PTH(1-34) were histomorphometrically evaluated in both cancellous and cortical bone tissues of axial and appendicular skeletons of parathyroidectomized and osteopenic rats. Osteopenia was induced by hemicordotomy immobilization and by estrogen depletion as a result of ovariectomy. The rats received intramuscular injections of 50 units (15 micrograms) of h-PTH(1-34) six times weekly during weeks 11 through 18 of the experiment. Significant restoration of cancellous and cortical bone volumes was observed in axial and appendicular skeletons of animals treated with h-PTH(1-34). The stimulatory effects of h-PTH(1-34) on osteoid surface, independent of eroded surface, in cancellous and cortical bone tissues, were clearly observed histomorphometrically. Mineralizing surface, mineral apposition rate and bone formation rate in cancellous bone tissues were markedly increased by h-PTH(1-34). It should be noted that h-PTH(1-34) increased trabecular thickness, but did not increase trabecular number. In conclusion, h-PTH(1-34) stimulated bone formation independent of bone resorption, and restored cancellous and cortical bone volumes in parathyroidectomized and osteopenic rats.