Spinal mobilization or manipulation techniques are frequently used by physiotherapists in the treatment of musculoskeletal disorders. Many of these techniques involve the application of a varying force to the affected joint. Despite the routine use of these techniques, there are no objective measures to quantify their use. This paper describes the principles of the instrumentation of a mobilization couch to enable measurement of the forces applied during mobilization of the lumbar spine. The couch was linked to a personal computer with a 286 processor and data card for data collection. The system was found to be reliable and sensitive over the range of forces applied during mobilization. It has potential for use in many situations where measurements of forces applied to the patient are required.