Type I cells of embryonic rabbit carotid bodies were cultured under normoxic (21% O2, 10% CO2, 69% N2) and hypoxic (5% O2, 10% CO2, 85% N2) conditions for two days. The mean membrane potential in the hypoxic cultivated type I cells (-27 mV) was significantly higher than in normoxic cultivated cells (-10 mV). The mean input resistance also had the tendency to increase under hypoxic conditions, from 19 m omega to 48 M omega. Results suggest that variations in membrane potential of type I cells due to oxygen pressure changes are an expression of the important role of these cells in oxygen sensing by the carotid body.