BACKGROUND Neuromuscular blocking agents reduce the human ventilatory response to hypoxia at partial neuromuscular block. It was hypothesized that vecuronium impairs carotid body chemoreceptor function during hypoxia. METHODS The effect of systemic administration of vecuronium on single chemoreceptor activity during hypoxia, as recorded from a single nerve fiber preparation of the carotid sinus nerve, was studied in seven mechanically ventilated New Zealand White rabbits during continuous thiopental anesthesia. During normoventilation, the isocapnic hypoxic chemosensitivity of the single carotid body chemoreceptor was measured at four levels of oxygenation; these measurements were repeated at six separate occasions: control recording before injection, after intravenous administrations of 0.1 mg and 0.5 mg of vecuronium, and then at three occasions during a 90-min recovery period. Chemoreceptor chemosensitivity during isocapnic hypoxia was expressed as a hyperbolic function: Chemoreceptor output (Hz) = a + b x PaO2(-1) (mmHg). RESULTS Chemosensitivity was reduced after both 0.1 mg and 0.5 mg vecuronium intravenous administration compared with control measurements; the hypoxic response curve was significantly depressed after both doses (P < 0.05). Notably, there was variation in the effect of vecuronium; some chemoreceptor preparations showed only minimal impairment, whereas some showed an almost abolished response to hypoxia. The chemosensitivity remained significantly depressed at 30 and 60 min but had recovered spontaneously at 90 min after 0.5 mg vecuronium. CONCLUSIONS It is concluded that vecuronium depresses carotid body chemoreceptor function to a varying extent during hypoxia and that the depression recovers spontaneously.