As a part of a major experimental study of forces in muscles and tendons it became necessary, as a preliminary step, to know the stress-strain relationship in human tendon. The studies reported herein give data from thirty tests on cadaveric human plantaris tendon in three states, i.e., moist, air dried and oven dried. Results are correlated with previously published results on tendon and with published strengths of human muscle and bone. Considerable new information on tendon strength is presented and several important deductive conclusions are given. The equipment and methods are described and illustrated and an appendix is given, showing results of the individual tests.