Total body vibration in supine, unanesthetized humans was studied at different frequencies up to 6.6 cycles/sec. In roughly 1/3 of 24 subjects, ventilation increased more than did metabolism, resulting in a lowering of alveolar CO2 pressure. The fall in arterial CO2 pressure was highly reproducible, persistent, and quantitatively related to the intensity of the vibratory stimulus. No isolated anatomical site for reception of the stimulus to ventilation was found. The response seemed rather to depend on the whole experience of vibration. While it could not be inhibited by direct voluntary control, vibration-induced hyperventilation disappeared with light general anesthesia. Hyperventilation tended to occur only in those subjects who characteristically had low resting respiratory frequencies and a low ventilatory responsiveness to CO2. Large individual differences in ventilatory response to CO2 which were observed at rest were found to disappear during vibration. The ventilatory response to vibration had many of the characteristics of a classical Pavlovian conditional response.