Estrogen may be involved in schizophrenia by inhibiting serotonin-1A (5-HT(1A)) receptor function. We examined the effects of estrogen pre-treatment on modulation of loudness dependence of the auditory evoked potential (LDAEP) and mismatch negativity by the 5-HT(1A) receptor partial agonist, buspirone. Using a double-blind, placebo-controlled, repeated-measures design in healthy female volunteers, we observed that buspirone treatment significantly increased LDAEP slope. Estrogen increased LDAEP slope on its own, and a further LDAEP increase by buspirone was not seen after estrogen pre-treatment. Similar results were observed for mismatch negativity, where buspirone caused a small increase of latency, although not amplitude, after placebo but not estrogen pre-treatment, which enhanced mismatch negativity latency on its own. These results are in line with our previous findings on prepulse inhibition showing an inhibitory effect of estrogen on the action of buspirone. Taken together, these data suggest that estrogen may inhibit 5-HT(1A) receptor-mediated disruptions of auditory processing.