The carotid body (CB) is the site in the body that triggers awareness of changes in blood oxygen pressure. Aging is characterized by a decrease in oxygen supply to tissues, in reduction of tissue Po2, and in the activity of several enzymes and metabolic factors. The ventilatory response to hypoxia is attenuated with aging related to the age-dependent structure modifications including the basal reduction of oxygen requirements. The aged CB shows an increase in extracellular matrix, a reduction in number and volume of type I cells, and a reduction in volume of mitochondria that was consistent with and similar to that during chronic hypoxia; this phenomenon seems to operate also during aging as shown by the reduced volume of mitochondria in the aged CB. During chronic hypoxia, CB hypertrophy is less evident in aged CB than in young CB. Therefore, hypoxia and aging seem to share some type of link at different cell sites. CB represents an experimental model adequate for studying aging processes because of its high blood flow and metabolism, and thus it serves as a means to understanding the oxygen modulation of the aging process.