The rupture of anterior cruciate ligament has been diagnosed by stress test, radiogram and diagnostic arthroscopy, but these methods have several disadvantages of lack of objectivity, exposure to radiation and risk of anesthesia. To eliminate these difficulties, the K-T 1,000 knee ligament arthrometer was used for the objective diagnosis in the injury of anterior cruciate ligament. We performed instrumented measurement of anterior-posterior laxity of the knee in 100 normal subjects by using the K-T 1,000 knee ligament arthrometer under the 15 lb., 20 lb. and maximum anterior pulls, and 20 lb. posterior push. The following results were obtained: 1. The mean anterior displacement at 20 lb.: 4.43mm The mean posterior displacement at 20 lb.: 2.30mm 2. The mean right knee-left knee difference in anterior displacement: 0.89mm 3. The mean anterior compliance index: 1.16mm So, we believed that a right knee-left knee difference and a anterior compliance index are sensitive measures of the integrity of the anterior cruclate ligament. And this test method was helpful for the diagnosis and objective recording in the injury of anterior cruciate ligament. This test method has following advantages: 1. There is no anesthesia risk. 2. The patient and examiner undergo no radiation exposure. 3. Diagnostic arthroscopy may be avoided. 4. Due to patient comfort, there is minimal muscle guarding.