We have recently developed an experimental system whereby pins inserted into the seventh and ninth caudal vertebrae of rat tails are used to load the eighth caudal vertebrae (C-8) in compression. In this model, a single 5-min period of dynamic loading, sufficient to induce strains within the range to which bones are exposed under physiological circumstances, stimulates lamellar bone formation in the cancellous bone of the vertebrae. The rapidity with which the increase in bone formation was induced raised the possibility that this bone formation might have occurred without prior resorption. To test the role of bone resorption in the response of the bone to mechanical stimulation, we compared the anabolic response to a single period of loading, of rats treated with 3-amino-1-hydroxypropylidene-1-bisphosphonate (AHPrBP) or vehicle. We found that mechanical loading caused a significant increase in dynamic and static indices of bone formation. The same indices were unaffected by AHPrBP, while the bone formation rate in the tibiae was reduced by AHPrBP. These results suggest that the increased bone formation induced by mechanical stimulation in the cancellous bone of rat vertebrae is not dependent on bone resorption.