Electromyography was used to investigate abdominal muscle activity during singing in four subjects, all of whom were trained classical singers. Results revealed regional differences in abdominal activation during the expiratory side of the breathing cycle. These were characterized by high-amplitude activity in the lateral region and low-amplitude activity in the middle region. For three subjects, amplitudes were higher in the lower lateral portion of the abdomen than the upper lateral portion. For the remaining subject, amplitudes were higher in the upper lateral portion than the lower lateral portion. Brief decrements in lateral abdominal activity often occurred in association with the onset of the inspiratory side of the breathing cycle. Findings support the concept that the abdomen plays an important role in the posturing of the chest wall for singing.