• Twelve patients with panic disorder and 11 control subjects received 24-hour ambulatory monitoring of heart rate, finger temperature, ambient temperature, and self-rated anxiety. No differences were found between groups in tonic levels of any measure or in their patterns of variation throughout the day. However, substantial heart rate increases and finger temperature changes did occur in panic attacks but not during control periods having equally high anxiety ratings. These measures may be useful in the diagnosis of panic disorder and in the assessment of treatment outcome.