Prostaglandin E₂ (PGE₂) at a dose of 10 mg/kg was administered orally to beagles used in a study of rib fracture and drill hole defect healing. Double fluochrome labels were given prior to surgical manipulation and before necropsy at 30 days. Bone remodeling was evaluated in trabecular bone of the fourth lumbar vertebra. There was a decrease in the number and extent of posttreatment labels (P<0.05) in the controls, with decreased mineral apposition rate (P<0.05) and decreased active bone formation rate (P<0.01). In dogs given PGE₂ for 30 days following surgery, the extent of posttreatment labels (P<0.05) and bone formation rate (P<0.01) were increased. There was no difference found, however, in static morphometric parameters, including osteoid and osteoblast-covered surface, indicating that the stimulation of bone formation may have been transitory and matrix synthesis had declined. In another group of dogs given PGE₂ for 5 days prior to surgical manipulation and between the first and second pretreatment labels, the extent of the double-labeled surface was increased (P<0.05) indicating an acute PG effect to sustain formation at remodeling sites. These studies show that PGE₂ given orally has a systemic effect on bone remodeling in vertebral trabeculae that involves the stimulation of formation activity.