Controversy exists on the relationship of knee ligament stability to knee injuries. Subjective evaluation of joint tightness or looseness has been proposed as a criterion for prescribing selective corrective strengthening or stretching exercises. Biomechanical studies of knee ligament stability were performed on 401 college football players from 1969 to 1971. Forty-three knee ligament injuries occurred during this period of time, 19 (44.2%) in "loose-jointed" players and 24 (55.8%) in "tight-jointed" players. Joint laxity tests were performed on 72 college football players; the distribution of college football players failing to perform each of the tests was quite different from that reported for professional football players. There was no relationship between the subjective joint laxity tests and the objective biomechanical tests of knee ligament stability. We conclude that it is not possible to predict knee injuries by subjective evaluations of joint laxity or by objective biomechanical knee ligament evaluations and that exercise programs based on subjective studies are therefore not sound.