One model of outcomes research is embodied in the Patient Outcome Research Teams (PORTs) supported by the Agency for Health Care Policy and Research (AHCPR). These teams were organized around specific clinical conditions and were to include literature synthesis activities, analysis of administrative databases, prospective cohort studies, and efforts to disseminate research findings to the larger practice community. For many, the rallying cry was "finding out what works in medicine." The experience of the low-back pain PORT illustrates some of the successes and limitations of this approach. This research team documented wide geographic variations in rates of back surgery at the international, national, and state levels. We also identified important variations in surgical outcomes according to the type of surgical procedure. In particular, operations involving spinal fusion were associated with higher short-term complication rates and costs, and long-term benefits remain unclear. Nonsurgical hospitalizations declined dramatically over the past decade. The research team summarized data to support the AHCPR's guideline efforts, and also to produce an interactive computer-based videodisc for helping patients make decisions about surgical or nonsurgical treatment. The team is disseminating data on practice patterns to surgeons in Washington State in an effort to reduce practice variability. Thus, this PORT has summarized knowledge for both patients and providers, identified important uncertainties in patient management, and helped to establish priorities for further investigation. It has generated new hypotheses about treatment effectiveness and safety and has developed new outcome measures that could be incorporated into future research. Unfortunately, we did not establish "what works" in medicine and would argue for a greater role of randomized clinical trials as part of the outcomes research portfolio.