The synovial membrane--the articular district of the s.i.--responds to pathogenic stimuli by cell hyperplasia, giving rise to the so-called pannus. This together with regression and haemorrhage, may lead to self-maintenance of the condition, over and above the persistence of the original insult, resulting in chronicity and degeneration. If performed when the disease is still limited to histiocyte hyperplasia, synovectomy is effective in both single-joint forms and systemic conditions, such as rheumatoid arthritis. These conclusions (already evident in the literature) emerged from a review of a series of 67 synovectomies and 29 tenosynovectomies performed between 1969 and 1978 for various joint and tendon afflictions (not including T.B.) marked by synovial hyperplasia.