In spontaneously breathing, pentobarbitone anesthetized cats, we recorded simultaneously the impulses in the chemosensory fibers of both carotid (sinus) nerves, to analyze the correlations between the frequencies of chemosensory discharges (f(χ)) and their activation ({df(χ)/dt}(a)) and deactivation ({df(χ)/dt}(d)) rates. We studied the chemosensory responses to brief exposures to hypoxia (100% N2; 5-s and 10-s) and hyperoxia (100% O2; 30-s), and intravenous injections of excitatory (NaCN 0.2-100 μg/kg) and inhibitory (dopamine hydrochloride 0.02-20 μg/kg) chemoreceptor agents. Hypoxia increased f(χ) with a high temporal correlation between frequency levels in both nerves. Prolonging hypoxic stimulation increased {df(χ)/dt}(d), with preservation of {df(χ)/dt}(a). Hyperoxic exposure produced highly correlated decreases in fχ in both nerves, but reduced correlation if df(χ)/dt. Increasing doses of NaCN produced analogous increments in f(χ), df(χ)/dt and their correlations, the {df(χ)/dt
