The tensile properties of the supraspinatus tendon were investigated in 11 shoulders from fresh cadavers. The tendon was divided into three longitudinal strips: anterior, middle, and posterior. Each specimen was mounted on a materials testing machine, with four fluorescent markers placed on both surfaces of the tendon strip. The positions of these markers were recorded during the test by two synchronized video cameras. Load-deformation and strain curves were determined, and the stress-strain curve, strength, and modulus of elasticity were calculated. The posterior strip was thinner in cross section than the others (p = 0.0355). The ultimate load and ultimate stress were significantly greater in the anterior strip (16.5 +/- 7.1 MPa) than in the middle (6.0 +/- 2.6 MPa) and posterior (4.1 +/- 1.3 MPa) strips (p < 0.0001). The modulus of elasticity also was significantly greater in the anterior strip (p < 0.0001), but there was no significant difference between the superficial and deep surfaces. It is concluded that the anterior portion of the supraspinatus tendon is mechanically stronger than the other portions, and it seems to perform the main functional role of the tendon.