Microfocal radiography records, with unusually good resolution, the detailed structural organization of cancellous bone. A textural imaging method, fractal signature analysis (FSA), was used to quantify the horizontal and vertical trabecular organization recorded within macroradiographic images of the spine of post-menopausal women and the tibia in osteoarthritic knees, and the analysis of variance method was applied to the wrist and hand of rheumatoid patients. Changes in trabecular structure were found to correlate with (i) body weight, age and bone mineral density in the lumbar spine of post-menopausal women; (ii) the degree of cartilage loss and age in the tibia of patients with knee OA; and (iii) analysis of variance quantified the extent of 'normal', osteopaenic and eroded bone in rheumatoid joints. Quantitation of cancellous bone organization can add significantly to our understanding of disease processes and effect of therapy in diseased joints.