Rapid alternating intrathoracic pressure changes caused by rapid breathing with partial obstruction to airflow caused a three to four fold increase in forearm blood flow whereas following the Valsalva maneuver the blood flow was decreased. Evidence is presented that these changes are brought about reflexly through alterations in vasoconstrictor tone. It is demontrated that the reflex changes are confined to skeletal muscle vessels, providing further evidence that the vasomotor centers controlling skin and muscle vessels can function independently.