This study tests the hypothesis that dehydroepiandrosterone (DHEA) stimulates formation of hippocampal CA1 spine synapses in ovariectomized rats. Subcutaneous injections of DHEA (1 mg/d for 2 d) increased CA1 spine synapse density by more than 50% compared with vehicle-injected animals. The effect of DHEA on CA1 synapse density was abolished by pretreatment with the nonsteroidal aromatase inhibitor, letrozole. DHEA treatment, with or without letrozole, had no detectable uterotrophic effect. These observations are consistent with the hypothesis that DHEA treatment may be capable of reversing the decline in hippocampal spine synapse density observed after loss of ovarian steroid hormone secretion. The blockade of the synaptic response to DHEA by letrozole, despite the lack of a uterotrophic response to this steroid, suggests that the hippocampal response to DHEA may be mediated via aromatization in the brain.