Conditioned inhibitors have been shown to be largely unaffected by non-reinforced exposure (i.e., extinction treatment). Although excitatory associations are readily diminished by extinction treatment, so-called inhibitory associations appear to be largely immune to them. In two fear-conditioning experiments with rats, it was found that a decrease in inhibitory control can result from a massive number of extinction exposures to the inhibitor. Experiment 1 provided evidence that extinction treatment attenuated negative summation between the potential inhibitor and a transfer excitor. However, the extinction treatment had no influence on responding to the original training compound, indicating that some stimulus-specific inhibitory potential remained even after massive extinction. Experiment 2 indicated that retarded excitatory acquisition to the inhibitory stimulus observed after extinction treatment of the inhibitor is no greater than that following a similar amount of stimulus pre-exposure without prior inhibition training (i.e., latent inhibition). The findings indicate that inhibitory associations can be extinguished with large numbers of extinction trials, but they appear to be much more resistant to extinction than excitatory associations.