Airway sensors play an important role in control of breathing. Recently, it was found that pulmonary slowly adapting stretch receptors (SARs) cease after a brief excitation following sodium pump blockade by ouabain. This deactivation can be explained by over-excitation. If this is true, mechanical stimulation of the SARs should also lead to a deactivation. In this study, we recorded unit activity of the SARs in anesthetized, open-chest and mechanically ventilated rabbits and examined their responses to lung inflation at different constant pressures. 47 of 137 units had a clear deactivation during the lung inflation. The deactivation threshold varied from unit to unit. For a given unit, the higher the inflation pressure, the sooner the deactivation occurs. For example, the SARs deactivated at 3.0±0.3 and 4.8±0.4 sec when the lungs were inflated to constant pressures of 30 and 20 cm H₂O, respectively (n=25, P<0.0001). The units usually ceased after a brief intense discharge. In some units, their activity shifted to a lower level, indicating a pacemaker switching. Our results support the notion that SARs deactivate due to over-excitation.