The knee joints of adult rabbits were subjected to daily one hour intervals of impulsive loading equivalent to their body weight at 60 cpm. They developed changes in their knee joints consistent with those of degenerative joint disease. The cartilage destruction was preceded by stiffening of the underlying subchondral bone. Numerous healing trabecular microfractures were associated with this increased stiffening. Similar microfractures have been observed in human specimens. The implications of these findings to bone remodelling and osteoarthritis are discussed.