Apparatus and methods for deactivating bronchial nerves and ablating smooth muscle extending along a bronchial branch of a mammalian subject to treat asthma and related conditions. An ultrasonic transducer (11) is inserted into the bronchus as, for example, by advancing the distal end of a catheter (10) bearing the transducer into the bronchial section to be treated. The ultrasonic transducer emits ultrasound so as to heat tissues throughout a relatively large impact volume (13) to a temperature sufficient to inactivate nerve conduction and ablate smooth muscle but insufficient to cause rapid ablation or necrosis of the surrounding tissues. The treatment can be performed without locating or focusing on individual bronchial nerves or smooth muscle.