The case histories of five young children are presented to demonstrate the radiological appearances of trauma to the spine thought to be the result of maltreatment by either parent or guardian. Four of the children were admitted to hospital within a period of three years, all being under the age of two years.

1. Experimental arthritis was induced in rats by the intradermal injection of modified Freund's adjuvant.

2. The granulation tissue occurring in and around the joints was examined with the electron microscope.

3. Intracellular collagen was demonstrated in many of the cells.

4. Collagen formation by these cells was studied by autoradiographic techniques using tritiated proline as a label.

5. The proline turnover was rapid, as most of the labelled proline had become extracellular one hour after its injection.

6. It was concluded that the collagen was present within the cells as a result of phagocytosis despite the fact that the cells had the electron microscopic features of fibroblasts.

Two brothers with osteochondrosis of the phalangeal epiphyses in the hand (Thiemann's disease) are described and the condition discussed.