SUMMARY1. A method for assessing the bronchodilator potency of sympathomimetics in anaesthetized cats is described.2. The bronchodilator actions of laevoisoprenaline, rimiterol and salbutamol, administered by cumulative intravenous injection, were assessed against bronchoconstriction produced by an intravenous infusion of serotonin. Rimiterol and salbutamol, by weight, were each about eight times less potent than laevoisoprenaline.3. The method allows the construction of reproducible dose‐response curves. It is relatively quick, and is especially useful when assessing the potencies of long‐acting sympathomimetic bronchodilat