Panic disorder (PD) and its complication agoraphobia are among the most common psychiatric disorders in this country (8). At present no objective laboratory tests exist to assist the clinician in making this diagnosis. There is now substantial experimental evidence that the acute anxiety attack (also known as a panic attack) is accompanied by precipitous and marked physiologic changes - principally cardiac and respiratory. We propose to extend our already acquired expertise in the laboratory assessment of panic attacks into the ambulatory, real life setting. This can be accomplished by the development of portable, non-invasive instrumentation and data analytic methods to allow the precise identification of the physiologic concomitants of an acute, "in vivo" panic attacks. In Phase I we will accomplish 3 goals: (1) development of a portable monitor to collect physiologic data, (2) demostration that patients can successfully denote panic attacks using an event marker on the monitor and that the physiologic data collected can reliably be accessed from this monitor and, (3) gathering of preliminary evidence that substantial and quantifiable physiologic changes occur during naturally occurring panic attacks. In phase II we will use the instrumentaiton and data routines to establish a definitive pattern of physiologic changes that accompany a panic attack by studying a large number of patients with panic disorder or agoraphobia with panic attacks. We hope to identify an unambiguous objective physiologic marker (s) for the panic attack that will assist clinicians in making more acurate diagnoses.