This study describes the developmental profile of specific aspects of cholinergic and purinergic neurotransmission in key organs of the peripheral chemoreflex: the carotid body (CB), petrosal ganglion (PG) and superior cervical ganglion (SCG). Using real time RT-PCR and Western blot analyses, we assessed both mRNA and protein expression levels for choline-acetyl-transferase (ChAT), nicotinic receptor (subunits α 3, α 4, α 7, and β 2), ATP and purinergic receptors (P2X 2 and P2X 3). These analyses were performed on tissue from 1- and 15-day-old, 2-month-old, and adult cats. During development, ChAT protein expression level increased slightly in CB; however, this increase was more important in PG and SCG. In CB, mRNA level for α 4 nicotinic receptor subunit decreased during development (90% higher in 1-day-old cats than in adults). In the PG, mRNA level for β 2 nicotinic receptor subunit increased during development (80% higher in adults than in 1-day-old cats). In SCG, mRNA for α 7 nicotinic receptor levels increased (400% higher in adults vs. 1-day-old cats). Conversely, P2X 2 receptor protein level was not altered during development in CB and decreased slightly in PG; a similar pattern was observed for the P2X 3 receptor. Our findings suggest that in cats, age-related changes in cholinergic and purinergic systems (such as physiological expression of receptor function) are significant within the afferent chemoreceptor pathway and likely contribute to the temporal changes of O 2-chemosensitivity during development.