Lactate infusions are anxiogenic in patients with panic disorder or agoraphobia with panic attacks, but few neuroendocrine profiles of this effect have appeared. The authors measured the number and intensity of panic symptoms and blood hormone levels during double-blind lactate infusions in 25 patients and 10 normal subjects and during placebo infusions in another five patients. Each patient was rechallenged with an identical infusate after chronic double-blind outpatient treatment with alprazolam or placebo. The results confirm the effectiveness of lactate infusions in evoking anxiety, extend previous hormone profiles of this maneuver, and indicate that chronic alprazolam treatment minimizes the neuroendocrine response to lactate challenges in patients with panic disorder or agoraphobia with panic attacks.