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Four series of experiments have been performed in normal subjects to determine whether face immersion gives rise to a reduction in ventilatory drive. Such a response might be advantageous, like the cardiovascular components of the 'diving response', in prolonging breath-hold diving. In the first series, ventilatory drive was measured indirectly as the maximal voluntary breath-holding time, starting each breath-hold at the same alveolar partial pressures and at the same lung volume. When the face was immersed in cold water, breath-holding times were increased by 14%. The breaking point occurred at a higher alveolar PCO2 and the rate of rise of PCO2 was not affected. Control immersions in warm water had no effect. In the second and third series, subjects lay prone and breathed either air or 5% CO2 through a valve in the bottom of a bowl. Minute ventilation was measured before, during and after 5 min of face immersion in cold water. Transient hypoventilations of 13% and 10% respectively were seen, accompanied by small rises in alveolar PCO2. In control experiments, immersion of the forearm in cold water produced the opposite responses. In the fourth series, a cold wet pack was applied to the face during moderate steady-state exercise. A small irregular hypoventilation was seen, but not in control experiments when a warm pack was applied. Face temperatures fell by about 10 degrees C in these experiments. No material changes were found in the temperatures of the inspired air or of the aural canal. It is concluded that face immersion in cold water causes a modest reduction in ventilatory drive in man. This appears to be a component of the 'diving response'.