Applying newer techniques to assess the reactivity of small peripheral airways, we studied the effects of saline and methacholine inhalation in patients with allergic rhinitis. The maximum midexpiratory flow rate (MMF) and the maximum terminal flow (MTF) were used to assess the degree of small airway obstruction. Four rhinitis patients (13 per cent) had abnormal baseline MMF and/or MTF and 12 patients (38 per cent) developed a decrease in MMF and/or MTF after saline inhalation. Twenty-one patients (66 per cent) responded to methacholine inhalation with a greater than 20 per cent fall in the MMF and/or MTF. This response was significantly different from that of the control subjects (p less than 0.01). The patients' hyperresponsiveness appears to be similar to that of asthmatic patients except that the obstruction is primarily limited to the airways.