A histomorphometric study was done on healing defects in the ribs of Beagles. A transverse fracture was made in the left 9th and 10th ribs. Beagles were given either ethanol vehicle (n = 6) or prostaglandin E2 (PGE2) orally (n = 5) for the 30-day period after surgical manipulation to time of necropsy. Double fluorescent labels were given to measure bone matrix mineralization. Two fluorochrome markers were used calcein before dogs were surgically manipulated and oxytetracycline HCl before they were killed. The two objectives of the present study were (1) to determine the effects of fracture on regional cortico-endosteal remodeling 2 cm from a fracture site in the ribs of Beagles; and (2) to determine the effects of orally administered PGE2 on the above condition. The results suggested that the fractured and the non-fractured ribs in either group show a similar static and dynamic remodeling during the first 30 days of healing. The activation frequency in the PGE2 group was increased in both fractured and non-fractured ribs more than in the non-treated group. Therefore, the systemic administration of PGE2 can activate and synchronize remodeling cycles among BMUs.