Eighteen patients who experienced frequent panic attacks were given a treatment derived from the literature on hyperventilation and anxiety. The treatment consisted of (i) brief, voluntary hyperventilation. This was intended to induce a mild panic attack; (ii) explanation of the effects of overbreathing and reattribution of the cause of a patient's attacks to hyperventilation; (iii) training in a respiratory control technique. Substantial reductions in panic attack frequency and in self-reported fear during a behaviour test were obtained after 2 weeks' treatment and these reductions occurred in the absence of exposure to feared situations. Further reductions in panic attack frequency were evident at 6-month and 2-year follow-up though interpretation of these results is complicated by the addition of exposure and other psychological treatments.