A variety of involuntary abdominal movements may result from peripheral insults or have a central origin. However, the spectrum of differential diagnoses can be broadened by this report of two patients whose involuntary abdominal movements were related to chronic use of haloperidol or sulpiride. Electromyographic studies revealed two patterns of muscle activity in these two patients. The first patient showed long-duration bursts of the thoracic and lumbar paraspinal muscles, causing repetitive backward tilting of the pelvis and downward shifting of the umbilicus. The second patient showed persistent contraction of the rectus and the external oblique abdominal muscles, causing sustained retraction of the abdominal wall and episodic jerking. Both patients improved dramatically after treatment with reserpine. We conclude that electromyographic study is useful in identifying truncal dystonia and abdominal dystonia, two variants of tardive syndrome.