Background: Anabolic responsiveness to teriparatide can be blunted or delayed in patients previously treated with alendronate. The extent of this effect is different for other antiresorptives. This study evaluated the early anabolic effects of teriparatide in postmenopausal women with osteoporosis previously treated with alendronate or risedronate. Methods: Patients treated for at least 24 months with alendronate or risedronate discontinued their bisphosphonate and received teriparatide for 12 months. The primary endpoint was a comparison of changes from baseline in N-terminal propeptide of type 1 collagen after 3 months between prior bisphosphonate groups. We also examined changes in other bone turnover markers, bone mineral density (BMD), and relationships between early changes in bone turnover markers and 12-month areal and volumetric BMD. Results: In the prior risedronate group, the N-terminal propeptide of type 1 collagen increase was significantly greater after 3 months of teriparatide than in the prior alendronate group (mean ± SE, 86.0 ± 5.6 vs. 61.2 ± 5.3 ng/ml, respectively; P < 0.001). Findings were similar for the other bone turnover markers. The changes in areal BMD and trabecular spine volumetric BMD were also greater in the prior risedronate group (P < 0.05). Early changes in bone turnover markers correlated with changes in trabecular spine volumetric BMD at 12 months (Spearman r = 0.45). Teriparatide was well tolerated. Conclusion: This nonrandomized but prospective study suggests that there may be differences in anabolic responsiveness to teriparatide as a function of the type of prior bisphosphonate exposure. Copyright © 2008 by The Endocrine Society.