A method for the estimation of quadriceps muscle strength has been developed, using strain gauges coupled to an electronic recorder. Preliminary work in 100 normal subjects delineated a range of strength values which have been related to weight, age, and sex. Comparison has been made with values obtained from patients with rheumatoid arthritis either during conservative treatment or following synovectomy of the knee joint. This method may prove a useful means of assessing physiotherapeutic techniques and their place in the attainment of muscle strength.