THE main physiological function of articular cartilage is to act as a bearing material. It consists of an organic matrix made of collagen, proteoglycans, non-collagenous proteins, lipids and cells that are swollen with water1,2. Its net fixed charge is negative and directly proportional in magnitude to its hexos-amine content at each depth3. When cartilage is compressed, interstitial fluid is exuded. This flow of fluid with respect to the solid matrix plays an important part in controlling various rheological properties of the tissue, such as its creep deformation under load4–11. Also, we have observed that measurable electrical potential differences are induced between the surface and deepest regions of cartilage when it is compressed. We report here our studies of this phenomenon to quantitatively relate the magnitude, sign and time dependence of the electrical potentials to the known features of cartilage mechanics and fluid flow11, that is, in terms of tissue structure, function and composition. Our results suggest that an electrokinetic mechanism is primarily responsible for the mechanical-to-electrical transduction response.