We measured purring in unrestrained intact pumas, cheetahs and domestic cats. Domestic cats, Felis silvestris f. catus, purr at a frequency of 26·3 ±; 1·95 (S.D.) Hz. The frequency at mid-expiration exceeds that at mid-inspiration by 2·4 ± 1·3 Hz. Purring frequency for individuals does not change with age. Purring can occur simultaneously with other vocalization. Two-channel acoustic measurements confirm that the primary mechanism for sound and vibration production is a centrally driven laryngeal modulation of respiratory flow. The diaphragm and other muscles appear to be unnecessary for purring other than to drive respiration.