Lively controversies related to panic disorder are under active investigation by research groups around the world. However, publications from different laboratories are difficult to compare since there has been little consistency in measures or even in types of assessment used to characterize and follow up patients. Participants in the recently convened National Institutes of Health Consensus Development Conference on the Treatment of Panic Disorder noted this problem and recommended establishment of procedures to ensure comparability of studies. We organized a conference of clinical investigators whose objective was to develop a standard assessment package. Participants represented biological and psychosocial panic disorder treatment research sites in the United States and Canada. The 2-day conference resulted in agreement on a battery of assessments considered essential for panic disorder studies. The purposes of our report are to disseminate the conference conclusions and to encourage adoption of the proposed standards by clinical researchers, journal editors, Public Health Service peer review committees, and the Food and Drug Administration. We also identify some problematic issues that require further work.