Pharmaceuticals account for a significant portion of health care costs and are an important target for attempts at cost reductions. While many techniques have been shown effective, most are resource-intensive, have demonstrated fatigue after the intervention is ceased, and have been directed at specific items rather than total charges. The authors designed a computerized program to feed back prescription charges. The intervention is easy to execute, inexpensive, and can be maintained indefinitely. The intervention was performed in a randomized, prospective, controlled trial with the medical residents of a large county hospital. The goal was to reduce total prescribing charges and produce a meaningful financial result. The intervention reduced the mean charge for a prescription by 6.7% (P less than 0.025), but with a long latent period and minimal impact on resident knowledge of drug charges. Significant differences were seen only at the end of the study. The program was viewed positively by the residents. The low cost of the intervention yielded a benefit-to-cost ratio in excess of 50:1. Because of computerization and ongoing patient and resident randomization at the study hospital, added costs of this randomized trial in terms of computer time and research assistance were less than $1,000.