The Stryker knee arthrometer was assessed in the environment of a nonspecialized National Health Serv ice clinic by junior doctors in training. Forty percent of proven anterior cruciate deficient knees had a meas ured anterior excursion of 2 mm or less compared with the normal side under the same circumstances. Twenty percent of normal knees tested showed more than this variation between knees when different observers were compared and also when the same observers were compared at three week intervals. There is thus a question about the use of this machine in a general orthopaedic clinic with different observers.