The ventilatory pattern at rest was examined in 28 healthy human volunteers by recording pneumograph tracings for a 1-hr period. The mean respiratory frequency was 19/min in females, 16/min in males, but with considerable variation both within and among subjects. The mean inspiratory phase accounted for one-third of the respiratory cycle, but this fraction increased with increasing respiratory frequency and decreased when the frequency slowed. Tidal volumes varied greatly, and sighing (breaths larger than three times the average tidal volume) occurred at an average rate of 10/hr for females, 9/hr for males. The possible physiologic role of periodic deep breaths, or sighs, in providing reinflation of atelectatic areas is discussed. respiratory cycle at rest; respiratory frequency and tidal volumes; periodic deep breaths (sighing); inspiratory phase as related to expiratory phase; normal breathing; hyperinflation; respiration; rate of respiration; pneumographic tracings Submitted on November 8, 1962