Teriparatide (rDNA origin) injection [recombinant human PTH (1–34)] stimulates bone formation, increases bone mineral density (BMD), and restores bone architecture and integrity. In contrast, bisphosphonates reduce bone resorption and increase BMD. We compared the effects of teriparatide and alendronate sodium on BMD, nonvertebral fracture incidence, and bone turnover in 146 postmenopausal women with osteoporosis. Women were randomized to either once-daily sc injections of teriparatide 40 μg plus oral placebo (n = 73) or oral alendronate 10 mg plus placebo injection (n = 73). Median duration of treatment was 14 months. At 3 months, teriparatide increased lumbar spine BMD significantly more than did alendronate (P < 0.001). Lumbar spine-BMD increased by 12.2% in the teriparatide group and 5.6% in the alendronate group (P < 0.001 teriparatide vs. alendronate). Teriparatide increased femoral neck BMD and total body bone mineral significantly more than did alendronate, but BMD at the one third distal radius decreased, compared with alendronate (P ≤ 0.05). Nonvertebral fracture incidence was significantly lower in the teriparatide group than in the alendronate group (P < 0.05). Both treatments were well tolerated despite transient mild asymptomatic hypercalcemia with teriparatide treatment. In conclusion, teriparatide, a bone formation agent, increased BMD at most sites and decreased nonvertebral fractures more than alendronate.