Federal guidelines for the treatment of acute low back pain were locally modified and made more specific. These guidelines were then programmed into a rule-based computer charting system which provides real-time advice regarding documentation, testing, treatment, and disposition of emergency department patients with this condition. In a time-series off-on experiment the system was shown to significantly improve documentation of the medical record and discharge instructions. There was little effect on the appropriateness of testing and treatment and the cost of care. These findings contrast with our previous experiment using a similar program for the care of health care workers exposed to body fluids. In that study both the appropriateness of care and the cost-effectiveness of care were substantially improved.