This paper describes a technique and apparatus for measuring the compressive modulus of articular cartilage under physiological loading rates. The compressive modulus is the most relevant property to the primary function of articular cartilage i.e., load carriage. It has been determined previously from measurement of cartilage deformation under slow or almost static loading conditions. The modulus was based on deformations occurring 2 s after the initial application of load which greatly reduces its relevance since in physiological conditions joint loading occurs within 10-150 ms. Five human knee joints have been used to test the apparatus before a major study is undertaken. The preliminary results from these joints show that the compressive modulus of articular cartilage measured within physiological loading time intervals was much greater than previously reported. The compressive modulus at 20 ms was in the range 4.4-27 MPa and was between 32 and 75 per cent greater than its value obtained at 2 s after loading.