The effects of prostaglandin E2 (PGE2) on bone growth were investigated in rats. Daily injection of PGE2 (1, 10, and 100 pmol) was given via local intraosseous route into the metaphysis of the left tibia for 14 days. The contralateral right tibia injected with vehicle and saline was for the control. The rats receiving no injection provided as normal control. The results obtained indicated that PGE2 slightly but significantly decreased the body weight increment without effect on tibial length. The most prominent effect of PGE2 was the increase of metaphyseal bone trabeculae by 45-81% in a dose-dependent manner. The microscopic examination revealed that PGE2 unequivocally increased the new woven bone formation. The bone cell population study showed no difference between the number of osteoblasts and osteoclasts in primary spongiosa of the PGE2-injected limbs and those of contralateral limbs. However, the numbers of osteoblasts and osteoclasts were markedly increased in secondary spongiosa in the PGE2-injected limbs. This finding confirmed a stimulatory role of PGE2 in the bone formation. The local intraosseous injection of PGE2 was proven to be a good model for the study of local growth factors on bone metabolism with a lower effective dose which eliminates the systemic side effects.