This study will compare the effectiveness of two popular and expensive non-surgical treatments for low back pain: spinal manipulation and physical therapy. In particular, spinal manipulation performed by chiropractors will be compared with the increasingly popular McKenzie method of physical therapy. Although these competing treatments are in common use, they have never been directly compared. Subjects will be recruited from two primary care clinics in a large health maintenance organization (HMO). Three hundred adult patients with uncomplicated low back pain that has not responded to 10 days of standard medical care will be randomized to chiropractic manipulation (n=132), physical therapy (n=132), or standard medical care supplemented by an inexpensive educational booklet (n=66). Subjects randomized to either manipulation or physical therapy will receive nine treatments over a four-week period following randomization. Symptom relief, functional status, restricted activity days and use of health care for back problems following the completion of treatment will be measured. Outcomes will be assessed through telephone interviews conducted 1, 4, 12, and 52 weeks after initiation of treatment. Medical records and the HMO's cost management information system will identify use of services and permit cost estimates. Analysis of variance techniques will be used to analyze the data. The results of this study will provide patients, physicians, managed health care systems and insurers with valuable information on the relative benefits and costs of these commonly used treatments for patients with low back pain.