The effects of the National Institutes of Health Consensus Development Program on physician behavior were investigated. The medical records of 2770 patients treated in ten hospitals throughout the state of Washington were reviewed to determine if quality of care improved with respect to 12 recommendations put forth by four consensus panels concerning surgical management of primary breast cancer, the use of steroid receptors in breast cancer, cesarean childbirth, and coronary artery bypass surgery. Care was studied during 24 months before and 13 to 24 months after each consensus conference. Results showed that the conferences mostly failed to stimulate change in physician practice, despite moderate success in reaching the appropriate target audience. It was concluded that the consensus development conference is an important educational tool whose effects might be enhanced by focusing on areas of practice that need improvement and by encouraging follow-up programs at the state and local level.