Intermittent hydrarthrosis in general has hitherto been regarded as a medical curiosity of unknown pathogenesis and in which treatment has been decidedly unsatisfactory.

Two typical cases of intermittent hydrarthrosis of the knee joint, of diverse etiology, are reported in which apparent cure was obtained following the operative removal of the synovial membrane.

The etiology in the first case was definitely traumatic, and the condition was associated with a fibrous tissue mass in the calf muscle, the probable origin of this mass being a hematoma of that region. The attacks were of nine months' duration, came on five weeks after the traumatism, and persisted despite aspiration, rest in bed, and autoserotherapy. No clinical hypersensitiveness could be demonstrated in the history or by exhaustive tests.

The etiology in the second case was obscure, but definitely related to menstruation. The semilunar cartilages had been removed at another hospital. She had had repeated aspirations without effect.

Despite the fact that rarely recurrences of this disorder may take place after long intervals, it is nevertheless felt that, on the basis of the above observations, synovial excision offers the best prospect for the cure of the condition.