Presents perhaps the best data on the use of chiropractic services from 1985-1991 in the United States and Canada. It is based on a sample of 130 chiropractors in five U.S. sites and 1 Canadian site. Sixty-eight percent of the selected charts from these chiropractors showed that care was sought for low back pain; 32% recorded care for other reasons. Eighty-three percent of all charts contained evidence of spinal manipulative therapy. Per episode of care across sites, there was greater than a twofold difference in the median number of visits related to low back pain. The chiropractic visit rates in the United States and Ontario are estimated to be about 100 and 140 visits per 100 person-years, respectively -- use rates that care twice those of estimates made 15 years ago. The great majority of patients receive care for musculoskeletal conditions of the back and neck, and number of visits per episode varies appreciably by site. This information should help us understand better what is happening in the use of chiropractic services in North America and should help in determining how to evaluate the quality of care and outcome of care for those services.