Acute Panic Inventory (API) scores were obtained from 26 normal controls and 89 patients with either panic disorder or agoraphobia with panic attacks before and during lactate infusions. Retrospective ratings of the patients' usual spontaneous attacks were much higher, by API, than ratings of moments of severe stress by the controls. Point of panic API scores, as well as increments of panic scores over prelactate scores, were higher for patients who experienced lactate panics than for both controls and patients who did not panic.