During treatment of out-patients suffering from DSM-III R panic disorder (PD) with and without agoraphobia, our attention was drawn to a high frequency of comorbid allergic reactions. In a controlled study, the prevalence of immediate type I reactions was determined in panic patients. Conversely, the prevalence of psychological disorders was recorded among allergic patients. Altogether, 79 out-patients with PD, 100 type I allergic out-patients and 66 controls underwent structured clinical interviews and tests for allergies. Of the patients suffering from PD, 70 per cent displayed type I immediate reactions (controls = 29 per cent). Vasodilatation (often approaching circulation collapse) is a frequently occurring allergic syndrome which is a very dramatic experience. Fifty per cent of the allergic patients showed mild to severe psychological disturbances (controls = 25 per cent); and 16 per cent had problems requiring treatment (controls = 9 per cent). Ten per cent of the allergic patients revealed PD (controls = 2 per cent). The association between PD and allergic (vasomotor) reactions was found to be highly significant. A functional relationship is hypothesized in terms of conditioning cognitive and vasomotor interactions during autonomic arousal.