This paper describes a method to determine the six degree-of-freedom kinematics of the human knee. A complete description of knee motion requires information on both the patellofemoral and the tibiofemoral joints. Six degree-of-freedom spatial linkages are used to determine the relative motion of each of the joints. One linkage is connected across the tibiofemoral joint and a second is connected across the patellofemoral joint. A three cylindric open chain model is then used to describe the motion of each of the joints. Sample kinematic data were developed using the Purdue Knee Simulator with natural knee specimens. The simulator is able to recreate anatomical loading of the knee during various activities. The natural specimens were mounted in the simulator with the linkages attached. Data were recorded for level walking and six degree-of-freedom kinematics were determined for the tibiofemoral as well as the patellofemoral joints.