Children undergoing continuous corticosteroid therapy become stunted in height. The mechanism of this inhibition of natural growth has been investigated in the lower femoral epiphysial growth plate of young rabbits on daily corticosteroid. The growth plate became narrow: fewer cells in the germinative zone gave rise to short widely-spaced chondrocyte columns, each with a reduced number of mature and hypertrophic cells; the pattern of trabecular bone in the metaphysis was also disturbed. After even small doses these changes develop very rapidly, and therefore impose a threat to the growth of children receiving treatment with corticosteroids.

1. Because of the controversy over the clinical effects of corticosteroids on joint tissues a series of experiments on the knee joints of rabbits was undertaken.

2. The articular cartilage of the distal femoral epiphyses of normalcontrols has been compared with that of rabbits treated daily either with cortisone or with methyl prednisolone systemically or by intra-articular injections.

3. The changes caused by intravenous papain and their subsequent recovery have been described, and the adverse effect of corticosteroids on recovery has been assessed.

4. The biological mechanisms involved are discussed, and as a result caution is urged in the administration of corticosteroids in the presence of progressive degenerative joint disease.