Physician overutilization of clinical laboratory tests has been well documented, but previous attempts aimed at changing this behavior have met with limited success. An educational feedback strategy was used to try to change physician behavior in ordering thyroid function panels (TFPs) in the Duke-Watts Family Medicine group practice. The rate of TFP ordering significantly decreased for three months following the intervention but rose to the preintervention level within six months. Senior residents appeared to be more responsive to the educational feedback than junior residents. Results obtained in this and other studies suggest that other factors compete with educational approaches in motivating physician behavior, and these override rational decision making.