In the future, the clinical application of bone morphogenetic protein (BMP) will be mainly in patients of advanced age. In this study, we examined changes in BMP activity due to aging in recipient rats. The bioassays were carried out with bovine bone matrix-derived BMP obtained by the Bessho's BMP purification method. The purified BMP with the atelopeptide type I collagen was implanted into the calf muscles of 5-, 10-, 20- and 40-week-old Wistar rats. Three weeks later, soft X-ray and light-microscopic examination disclosed new bone formation in each aged recipient rat. Bioassay revealed decreasing ALP activity and Ca content as the recipient rats became older. However, bone induction was detected even in the 40-week-old Wistar rats. These results suggested that the bone inducing activity of BMP decreases proportionately as the recipient ages. Nevertheless, BMP offers considerable possibilities for clinical application in patients of advanced age.