A project to pursue standardization of the performance and interpretation of transcranial Doppler studies was designed. Phase I consisted of a national survey of the current practice of transcranial Doppler in the United States. From 200 ultrasound laboratories surveyed about the use of transcranial Doppler, 60 completed questionnaires were returned. The results show that further standardization of transcranial Doppler performance and interpretation is necessary, and provide the foundation for phases II and III of the project.