A method was developed for measuring the rotatory laxity of fresh knee-joint specimens by automatic cyclic rotation. Twenty-seven cadaver specimens were studied at an angle of 25 degrees of flexion. Primary laxity was defined as the rotation for a low torque of ± S kilograms force-centimeter Secondary laxity was the additional rotation at the extremes of motion at the maximum torque applied. There was a wide variation in laxity among different knees, with no discernible correlation with age, sex, race, or body build The menisci played a part in controlling laxity, particularly in the primary laxity phase at high torque. The collateral ligaments were twice as effective as the cruciate ligaments in controlling rotatory laxity. Axial load on the knee greatly reduced rotatory laxity. A 100-kilogram load reduced rotation to 20 per cent of that at zero axial load.