Rice bodies obtained from a young man with juvenile rheumatoid arthritis were found by light and electron microscopy to contain cells that appeared viable. The majority of these cells closely resembled type B synovial lining cells. Type A-like cells were also seen. The cells contained few mitochondria but often much lipid and glycogen, observations which suggested a dependence on anaerobic metabolic pathways in the avascular synovial fluid environment. Cells within the rice bodies lay in a matrix of collagen fibres, fibrin, and amorphous material. The source of the collagen appeared to be the cells themselves. The relatively normal appearance of the cells suggested that they were protected from many of the inflammatory stimuli present in rheumatoid synovia. This 'reversion' towards a normal appearance suggested that the stimuli inducing chronic rheumatoid inflammation might not originate in the synovial lining.