[en] To determine the effects of the dry powder inhalation (DPI) of ipratropium bromide (ipratropium) on the airways of health horses and the dose-response curve in horses suffering from chronic obstructive pulmonary disease (COPD) by means of pulmonary function tests, five healthy horses were first studied. Ipratropium (2400 micrograms ipratropium horse-1) was contained in gelatine capsules and administered using a dry powder device connected to an adapted face mask. Pulmonary function tests were recorded before inhalation and 15 and 60 min after inhalation. No modification of pulmonary function was observed. The airway response to ipratropium DPI was then determined in six horses suffering from COPD. To induce airway obstruction, the horses were bedded on straw and fed hay. When the maximal change in pleural pressure during tidal breathing exceeded 1.96 kPa, pulmonary function tests were recorded before DPI, and 15 and 60 min post-inhalation. Placebo (six capsules horse-1) or ipratropium (600, 1200 and 2400 micrograms horse-1) was administered in a randomized order to each horse using the dry powder device and the adapted face mask. Neither ipratropium nor placebo DPI affected respiratory frequency (f) or tidal volume (VT). Inhalation of 600 micrograms ipratropium horse-1 resulted in a delayed decrease of total pulmonary resistance (RL) whereas dynamic compliance (Cdyn) was improved (although not significantly) at both times of measurement when compared with values following placebo inhalation. Simultaneous decreased RL and increased Cdyn, was observed within 15 min after DPI of 1200 micrograms ipratropium horse-1 and persisted for the 1 h duration of the experiment. Doubling the dose also improved pulmonary function but not significantly more than following inhalation of 1200 micrograms ipratropium. No systemic side effects were observed in either group of horses.